• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    A Hybrid Virtual Cloud Learning Model during the COVID-19 Pandemic

    2021-12-16 06:39:24ShaymaaSorourTamerKamelandHananAbdelkader
    Computers Materials&Continua 2021年3期

    Shaymaa E.Sorour,Tamer M.Kamel and Hanan E.Abdelkader

    1Department of Educaion Technology(Computer Teacher Preparation),Kafrelsheikh University,33516,Egypt

    2Department of Educaion Technology,Kafrelsheikh University,33516,Egypt

    3Department of Computer Teacher Preparation,Mansoura University,35516,Egypt

    Abstract: The COVID-19 pandemic has affected the educational systems worldwide, leading to the near-total closures of schools, universities, and colleges.Universities need to adapt to changes to face this crisis without negatively affecting students’performance.Accordingly,the purpose of this study is to identify and help solve to critical challenges and factors that influence the e-learning system for Computer Maintenance courses during the COVID-19 pandemic.The paper examines the effect of a hybrid modeling approach that uses Cloud Computing Services(CCS)and Virtual Reality(VR)in a Virtual Cloud Learning Environment (VCLE) system.The VCLE system provides students with various utilities and educational services such as presentation slides/text, data sharing, assignments, quizzes/tests, and chatrooms.In addition,learning through VR enables the students to simulate physical presence,and they respond well to VR environments that are closer to reality as they feel that they are an integral part of the environment.Also,the research presents a rubric assessment that the students can use to reflect on the skills they used during the course.The research findings offer useful suggestions for enabling students to become acquainted with the proposed system’s usage, especially during the COVID-19 pandemic,and for improving student achievement more than the traditional methods of learning.

    Keywords: Virtual cloud learning environment; virtual reality environment;rubric assessment; COVID-19; critical challenges

    1 Introduction

    The global pandemic of COVID-19 has led to calls for social distancing.Among the regulations instituted to fight the virus, citizens have been told to remain indoors, where they are often idle, leading often to mental stress.Staying mentally engaged is one way to reduce mental stress, and as such online learning can play an important role in such an engagement.Indeed,online learning is considered to be the best solution to engagement during the pandemic.Teachers can use virtual classrooms to teach from home with tools that make online sessions effective and efficient.Pandemics often compel learners to stay at home for long periods of time and obstruct the teaching-learning process [1,2].Therefore, to face the COVID-19 pandemic, educational institutions must adopt the best methods of providing inexpensive and highly efficient services using academic tools and research practices.The UNESCO [3] lists educational applications, platforms,and resources as distance learning solutions that aim to help parents, teachers, schools, and school administrators facilitate the student-learning process and provide social care and interaction during periods of school closure.Most of the solutions devised are free and many cater to multiple languages.They tend to have a wide reach, a strong user-base, and evidence of impact.They are categorized based on distance learning needs, while most of them offer functionalities across multiple categories.One item on the list is Digital Learning Management Systems, which contain Moodle as a community-driven and globally supported open learning platform, as an essential cloud computing tool.

    Cloud Computing Services (CCS) have received notable attention in various information technology fields.They utilize many services as structured storage systems as well as social networking and distributed file systems to ease data sharing, storage, multi-format content, and synchronization [4,5].For this reason, many educational institutions have adopted CCS technology, which makes it easy for users to reinforce their educational expertise via services that can be accessed anywhere and anytime without having to worry about working cloud services or their location [6-8].

    According to the existing research, using CCS has several benefits.Firstly, CCS supply e-learning services like simulations, virtual worlds, and video streaming in Massive Open Online Courses.They supply teachers and students with useful methods from computing resources for laboratories and lectures based on specific learning needs.Teachers can design and implement virtual computers (also called Virtual Machines or VMs) with pre-installed software to deploy computing laboratories quickly [9-11].Secondly, cloud computing is cost-effective and therefore useful when resources are unavailable or scarce, and academics gain a positive and valuable experience from using it.Thirdly, CCS technology can support students and academics.Fourthly, it allows users to share, edit, process, and save massive amounts of data in educational environments and to use teaching and learning [12,13].Lastly, CCS create a personalized learning environment or virtual learning and teaching communities [14,15].

    In this research, a hybrid modeling approach with CCS and VR was applied in a Virtual Cloud Learning Environment (VCLE) system.This approach and VCLE system were intended to overcome problems that students may face in learning during computer maintenance courses and to avoid obstacles caused by the students’physical absence from university during the COVID-19 pandemic.Under the circumstances, the students may struggle to identify errors in their learning or practice efficiently, and they may lack many services that can help them learn using traditional methods.The proposed system helps teachers to recognize problems, such as when students make mistakes, by analyzing student submissions.It also permits the teachers to enhance teaching sources and tools [16].

    The VR environment is a collection of the educational methods, intended to improve students achievement by making computers and Internet as an essential part of the educational process,such as by providing web-based access to classrooms, grades, and reports [17].Thus, VR systems facilitate many educational procedures for both students and teachers in the following areas:management, connection, participation, administration, and syllabus preparation [18].The main goal of using these environments in this research is to provide students with valuable data as well as interaction with the subject, and to generate an optimal model of learner’s activities [19-21].

    In this situation, learners feel connected to the environmental components [22].In this research, VR was applied with CCS to explore student-learning outcomes.The proposed system enables both teachers and students to share information and introduce teaching opportunities that can enhance productivity, improve ease and support traditional teaching-learning methods.The system aims to improve students’ability to learn more profoundly.There are specific student characteristics that can be associated with students’success rate and performance improvement.Our goal is to help students to perform well and provide all the necessary educational services through the VCLE system.Also, the feedback process was added to help improve students’learning process during the course [23].Furthermore, many CCS and tools were employed in the VCLE to offer innovative opportunities for education.Rubric assessments were used to estimate students’performance and skills in the educational environment.Rubrics are highly regarded as tools that increase validity and accuracy in assessment [24] because they provide clear evaluation criteria, data quality, and scoring plans [8].In this research, we also used evaluation criteria as a kind of rubric evaluation to estimate students’skill performance in computer maintenance to increase the validity and accuracy of achieving the practical goals.

    To improve student performance and develop a practical implementation, this study examines the use of the VCLE system with a rubric assessment, applied with the following objectives: (i)To increase student satisfaction with learning environment, (ii) To use Virtual Reality (VR) videos to encourage students to learn more deeply, and (iii) To improve student performance by eliciting feedback in consecutive lectures and tracking students’learning situation.

    The rest of the paper is organized as follows.Section 2 provides an overview of the related work.Section 3 explains the proposed VCLE system with a rubric assessment.Section 4 introduces the rubric assessment for the Computer Maintenance course.Section 5 discusses the main experimental results.Finally, Section 6 concludes the paper.

    2 Literature Review

    2.1 Virtual Reality and Cloud Computing in Learning

    E-learning employs a variety of virtual learning tools, and cloud computing is often discussed as a way to provide assistance to e-learning frameworks.Fig.1 shows the cloud computing structure for e-learning applications and provides some examples of e-learning approaches to the cloud computing applications [25].E-learning in the cloud is considered to be an educational program and a service.Content can be published very quickly, and there are a few hardware requirements for users.Moreover, it reduces the burden of maintenance and support on the educational institution and allows users to receive the latest system updates without paying extra fees and to share main resources [26].E-learning systems are currently being developed at a fast rate.Accordingly, some challenges that arise include optimizing resource calculation, storage communication requirements, and handling requests for dynamic synchronization.

    Hence, the importance of cloud computing as a platform meets scalable and cost control requirements.Various scientific contributions address the importance of employing CCS in education.For instance, Liao et al.[27] described that cloud services have already been approved in the educational sector, where various educational institutions in the United States have emphasized the ability of cloud computing to improve efficiency, cut costs, and facilitate learning in addition to research.Derboven et al.[28] showed improvements in students’collaboration and learning experiences when they used education-based cloud services like the Google App Education, which includes Google, email and document sharing, and provides benefits similar to those of its rivals(e.g., Microsoft).Derboven et al.[28] described the virtual learning environments used by many higher educational institutions.A detailed explanation was provided on how teachers adapted to the learning environment to meet their needs, using a mixture of semiotic, multimodal analysis and an in-depth study of users with 24 participants.

    2.2 Effect of Rubric Use on Student Performance

    Barney et al.[29] indicated that student outcomes were affected by both rubrics and oral feedback.Their experiment, conducted in the software engineering course, led to statistically significant results.The use of rubrics was found to decrease the number of student complaints and questions related to grades.A rubric was designed to enhance students’understanding and awareness of the nature of multimedia presentation slides [30].When compared against a control group, students who used the rubric achieved a higher score, and their multimedia illiteracy was reduced.In the study, undertaken [31] students acknowledged using a rubric as a “recipe” that guided them through standard criteria.Students in the control and experimental group assessed their own self-organization, which was considered in terms of its effect on their academic performance.The results indicated that students, who used the rubric performed better compared to those who did not use it.They had greater accuracy in self-evaluation, higher performance scores,and higher scores for self-regulation, as it appears that the rubric aided their self-evaluation [32].Other factors also contributed to the rubric’s utility.Another study used four sources to collect information about the use of rubrics in higher education: Interviews, observations, questionnaires,and documentary analyses.Three case studies from different disciplines were presented, each indicating the importance of students using a rubric to increase their progress and improve their learning efficiency.The students found that the criteria used in the rubric were understandable and useful [33].

    In summary, the following statements can be made:

    ? Several studies have emphasized the importance of both VR and CCS in various educational fields.The incorporation of this technology can improve learners’competence and increase their academic level.

    ? Free services provided by the cloud can be used to create an active learning environment that is interesting for students and meets their needs, which in turn helps to reduce the cost of the infrastructure.

    ? Previous studies reviewed the challenges and opportunities that can be focused to use VR technology and CCS in a way that fosters student creativity.

    ? Rubrics are useful assessment tools that help decrease the number of student complaints and questions related to grades and increase students’skills, particularly in practical fields.

    3 Proposed Framework

    This study designed and utilized the cloud as a SaaS service model [34,35] to combine new services and create a new VCLE system to increase user satisfaction and improve the studentlearning environment in a Computer Maintenance course.The study also adopted Moodle, which is one of the most popular and applied VCLE systems in the educational institutions.

    UNESCO [3] has listed some educational applications, platforms, and resources as distance learning solutions that aim to help parents, teachers, schools, and school administrators, facilitate student-learning and provide social care and interaction during the periods of school closure.Fig.1 presents the proposed system, where the system administrator can upload learning tools such as lecture slides, VR, assignments, quizzes, audio, and video.Each lecturer can allocate tasks and items based on the nature of the materials and students’needs.Only students who are enrolled in the module can access the materials and activities.They can submit assignments, send or receive chats, participate in workshops, and contribute to the wiki.The system allows lecturers to organize and manage a virtual class, and provides students with feedback.Most Moodle courses have an IT specialist or system administrator, who has downloaded the open-source code,installed and set it up on a server, and managed all the services in the system.

    Figure 1: Proposed system framework with critical challenges and factors for use in online learning during the COVID-19 pandemic

    The proposed system is designed to serve educational institutions by combining helpful services to make users interested in finishing their tasks appropriately and efficiently.Accordingly, this study provides many VR videos to teach students more deeply detailed knowledge of computer hardware and components.The contents show students how to fix malfunctions, which cannot be seen or dealt with in the traditional learning method.

    3.1 Participants

    The sample consisted of 100 students in the Department of Educational Technology-Computer Teacher Preparation at Kafrelsheikh University.The students were enrolled in a Computer Maintenance course.They were divided into two groups of 50 students each: Group 1 studied using the VCLE system, and Group 2 learned with the traditional method (presentation slides accompanied by the lecturer’s audio comments).The main subject from Lessons 1-8 was computer hardware; the students learned about the malfunctions of different hardware components (e.g., power supply, hard disk, motherboard, DVD, processor, RAM, Cards) and how to fix bugs.There is often great difficulty in learning using the traditional method, as it is difficult for students to practice and detect problems.Next, from Lessons 9-15, the students learned about computer software, including Windows setup, hard disk partition, Hiren’s boot, and antivirus programs.However, our system is concerned with Lessons 1-8.

    3.2 Proposed System Architecture

    3.2.1 Proposed System Contents

    The proposed system contains of the following components:

    ? Users: The users are students using the VCLE system and lecturers, who are responsible for developing, organizing, and controlling learning materials, exercises, and other contents.

    ? VCLE: The VCLE is a new Moodle system that provides variety in terms of the location of services and the way that students can access the service.It also allows users to observe activities, and select and arrange data.

    3.2.2 VCLE System Structure

    (a) The first step was to create a website for the Computers Maintenance course and adjust all the related settings such as the course full and short name, course start and course end,description, appearance, and course format.

    (b) The objectives for the course and sub-objectives for each lecture were added to the system.Every student had a username and a password to access the system and navigate all the components.Course topics were divided into lectures, virtual videos, single activities,quizzes, tests, and a standard format.

    (c) Every lecture contained the following:

    ? Lecture contents (text, presentations, virtual videos, images, tables, and charts)

    ? VR videos with 3D Max that illustrated the subject and enabled students to imagine what might happen in a real-life situation.Fig.2 displays some snapshots of the VR videos.Fig.3 presents the VCLE system.Also, each lecture was divided into several videos to teach the internal structure of each component, including how it works and its various faults.Also discussed was how to identify subtle errors and fix the malfunction.

    Figure 2: Snapshots of VR used in the computer maintenance course during the COVID-19 pandemic

    Figure 3: Interface of the VCLE system

    (d) A variety of questions, such as multiple-choice, fill in the missing words, drag and drop into text, drag and drop into an image, true or false, and other types.These trained the students with automatic feedback after each lecture.

    (e) Chat rooms available at a specified time.Students could discuss issues related to the lessons or the system with their lecturer.Other activities available in the system were assignments,workshops, and a wiki.

    (f) Quizzes.The students could train on several quizzes after each lecture, and the system supported them with adequate automatic feedback.

    (g) Information on student’s last access to the course, current status, and grades.The system could report for each student individually or all students.

    Tests and grades.After finishing the learning process for each objective, students could take the test and receive their final score.All grades were saved in the system, and the lecturer could save and review all students’answers to follow their progress.

    3.2.3 Rubric Assessment for the Computer Maintenance Course

    Rubrics are documents that indicate the expectations for a specific task or set of tasks, via listing the criteria of assessment.They can be used to estimate multidimensional performances [36-38].

    In this research, two types of rubric criteria were used to estimate students’skill performance in the Computer Maintenance course.According to the instructions of the Ministry of Higher Education, students shall take their final exams on-site at their university.Students shall come to the university twice before the practical test to be observed in all practical lessons, according to the announced decisions.Tab.1 shows the first type, “General Rubric for the Computer Maintenance Course.” Tab.2 presents the second type, “A Specific Rubric for Disassembly and Reassembly of the System Unit.”

    3.2.4 Rubric Assessment Validity and Reliability

    After we had prepared the General Rubric (7 criteria), and the Specific Rubric (5 criteria)for the Computer Maintenance course, we measured their validity.The validity is an evaluation of how well the rubric measures what it is designed to measure [39,40].This study used referee validity to measure the validity of rubrics.The rubrics were given to specialists in computer science, curricula, and teaching methods to ensure that the criteria were suitable to the specific goals of the study.Fig.4a shows the opinions of the specialists, who were given the General Rubric specialists; Fig.4b shows the opinions of those who received the Specific Rubric.

    Figure 4: (a) Specialists’ opinions on the general rubric (b) specialists’ opinions on the specific rubric

    Table 1: General rubric for the computer maintenance course

    Table 2: Specific rubric in disassembly and reassembly of the system unit

    3.2.5 VCLE System Mechanism

    ? Before the lecture time, the system sends emails to all students as notifications about the lecture topic and schedule.

    ? Each student is logging in the VCLE system using his username and password.

    ? The system is opened, and students can meet his colleagues and teacher in the chatroom.

    ? The lecturer can download his lecture and explain the overall objective and sub-objectives.Also, the lecturer allow students to watch all the required videos, activities, audio, reading content, to communicate with students and excitingly connect the subject.

    ? Students can use raise hand tool if they have a question, and the lecturer answers their question.

    ? Before the lecture ends, the lecturer proposes a summary of the course then asks some questions to students.

    ? Students can sign in to online-specific assignments such as responding to lecturer-posed questions in a discussion board, or answer the quiz after the lecture.

    ? VCLE system provides dashboards for the lecturer to easily help them supervise their students online, furthermore predicts at-risk students who might fail to pass their final exams.

    ? The use of rubric assessments might help predict students with lower performance and who can be at risk of failing to pass their final exams; and, provides real-time interventions, like notifications, by providing supportive learning content for students while learning.

    4 Results

    This section is divided into three subsections.The first compares the VCLE group with the traditional group, the second illustrates the effect of lecture quizzes, and the third describes the rubric assessment.First, we checked the homogeneity of variances for the data, Levene Statistic=0.488.A descriptive quantitative analysis was performed using SPSS 23.00.

    4.1 VCLE System

    The difference in the pre-test scores between the two groups was not significant, while the t-test between the two groups in the post-test (t=13.029,p <.01) was significant.Meanwhile,the difference between the pre- and post-test scores was significant for the experimental group(t=-3.029,p <.01) as well as the traditional group (t=-48.821,p >.05).This means the VCLE activities were helpful to stimulate student-learning achievement.

    A pair sample t-test was used to analyze the pre- and post-test scores for each group, as shown in Tabs.3 and 4.The mean difference was 9.50.The correlation of the pre-test was 0.67,p <.01, and there was no significant enhancement in the pre-test, wheret=1.159.The mean,SD, and SEM were 0.16000, 0.97646, and 0.13809, respectively.In the post-test, the correlation was -.068,p >.05,t=13.029.The mean, SD, and SEM were 9.50000, 5.15574, and 0.72913,respectively, and is a significant enhancement in the post-test for the VCLE group wherep <.01.

    Tab.5 shows the means and SDs of the post-test for the two groups using an independent samples test.Students in the VCLE group gained significantly higher scores on the post-test(F 102.2,p <.01).They demonstrated better levels of improvement in the Computer Maintenance course than their counterparts in the traditional group.

    Table 3: Descriptive statistics for the traditional and experimental groups: pre- and post-test scores

    Table 4: T-test results for the VCLE and traditional groups

    Table 5: T-test results for the post-test scores of the VCLE and traditional groups

    4.2 Cloud-Based VCLE System Using Lecture Quizzes

    Tab.6 shows the one-way ANOVA results for the two groups using lecture quizzes (4 tests).The VCLE group achieved the most positive and high mean scores on all quizzes.Figs.5 and 6 show students’grades on all the lecture quizzes for the two groups, and Fig.7 presents the overall quiz average between the two groups.

    Table 6: ANOVA results using lectures quizzes

    Figure 5: Student grades on the post-test and lecturer quizzes for the VCLE group

    Figure 6: Students’degree in post-test and lecturer quizzes for traditional group

    Figure 7: Overall quizzes average between the two groups

    Table 8: ANOVA results for the rubric criteria according to three assessments

    4.3 Cloud-Based VCLE System Using the Rubric

    Tabs.7 and 8 show the means and SDs for each rubric criterion using three assessments.Responses from the VCLE group were generally the most positive, and the highest mean score was achieved by the VCLE group for Criterion 5 (9.98), indicating that students in the VCLE group were better at identifying and solving malfunctions than were their peers in the traditional group.Also, the VCLE group did the best oral presentations; the students demonstrated self-efficacy.

    Tab.9 shows the bivariate correlation for student performance between the post-test and rubric assessments, and Fig.8 illustrates the relation in the VCLE group in Assessment 3,using criteria (a) to (g).The VCLE group had positive relationships in all evaluations, and the traditional group had negative connections in Accuracy, Organization (Presenter and Oral Presentation), and Appearance (Presenter).

    Tab.10 shows the Means and standard deviation results, and rubric assessment for disassembly and reassembly of the system unit, and Tab.11 presents one-way ANOVA results.The results indicate that responses from the VCLE group were generally the most positive, and the high mean score achieved by the VCLE group for all criteria.Also, this is significant for functionality, senses and timeliness using the VCLE.The overall results indicate that the VCLE group participants interacted with the cloud computing system more frequently than once.Also, VCLE students have the capability of achieving maintenance course goals than the traditional method.

    Table 9: Bivariate correlation for students’grade post-test and rubric assessments

    Figure 8: Correlation between student grades on the post-test and rubric assessments for the VCLE group for assessment 3

    Table 10: Means and SDs for the specific rubric for disassembly and reassembly of the system unit

    Table 11: Descriptive statistics for the specific rubric for disassembly and reassembly of the system unit

    5 Conclusion

    COVID-19 has entered the world scene as a deeply shaking, worldwide pandemic.This paper emphasizes how online learning is beneficial during the pandemic and presents a VCLE system that connects CCL and VR environments to improve student’s performance and solve the practical problems that occur in a Computer Maintenance course.CCS and VR were examined to holistically quantify students’performance and activities in the learning environment.The experiment results have shown significant differences between the groups and assessments.Specifically, the VCLE group demonstrated higher performance in comparison with the traditional group.The upper-grade groups were also distinguished through the results.On the contrary, we can conclude that the VCLE approach may contribute to transforming students’views on learning computer maintenance from one of memorizing facts or practicing drills to a more advanced perspective that includes seeking deeper understanding, identifying issues, and problem-solving.Finally, the findings represent a novel contribution to university policymakers for utilizing the proposed system to ensure successful usage of e-learning.The proposed system identifies the factors that support the adaption of the e-learning system.Furthermore, research should be performed to discuss the deficiencies of this paper.First, it is necessary to communicate with each student and understand the determinants that impact students’academic achievement (e.g., students’negative or positive attitudes, their attempts) which will help the lecturer to understand the educational scene.Second,we should build an intelligent system that gives automated feedback to enhance awareness of the online learning system that includes student performance and prediction model.

    Funding Statement:The authors received no specific funding for this study.

    Conflicts of Interest:The authors declare that they have no conflicts of interest to report regarding the present study.

    a级毛片黄视频| 成年人免费黄色播放视频| 你懂的网址亚洲精品在线观看| 亚洲av中文av极速乱| 日韩大片免费观看网站| 精品国产国语对白av| 999精品在线视频| 日韩视频在线欧美| 制服丝袜香蕉在线| 久久久久视频综合| 国产精品熟女久久久久浪| 午夜精品国产一区二区电影| av有码第一页| 国产精品秋霞免费鲁丝片| 中国国产av一级| 日韩亚洲欧美综合| 建设人人有责人人尽责人人享有的| 欧美xxxx性猛交bbbb| 国产伦精品一区二区三区视频9| 国产欧美另类精品又又久久亚洲欧美| 免费av中文字幕在线| 亚洲欧美清纯卡通| 久久人人爽人人片av| 亚洲av在线观看美女高潮| 国产成人午夜福利电影在线观看| 国产免费现黄频在线看| 亚洲精品,欧美精品| 国产一区亚洲一区在线观看| 热re99久久国产66热| 久久精品久久久久久久性| 久久久a久久爽久久v久久| 欧美变态另类bdsm刘玥| 成人亚洲欧美一区二区av| 日本av免费视频播放| 国产伦精品一区二区三区视频9| 夫妻午夜视频| 美女cb高潮喷水在线观看| 免费日韩欧美在线观看| 在线亚洲精品国产二区图片欧美 | 午夜视频国产福利| 亚洲性久久影院| 精品国产露脸久久av麻豆| 久久99蜜桃精品久久| 日韩av免费高清视频| 亚洲,一卡二卡三卡| 国内精品宾馆在线| 性色av一级| 伊人久久国产一区二区| 欧美精品高潮呻吟av久久| 精品国产一区二区三区久久久樱花| 日韩不卡一区二区三区视频在线| 欧美日韩国产mv在线观看视频| 九九爱精品视频在线观看| av视频免费观看在线观看| 人人妻人人澡人人爽人人夜夜| 99热6这里只有精品| 亚洲人与动物交配视频| 性色av一级| 高清在线视频一区二区三区| 国产成人午夜福利电影在线观看| 国产高清不卡午夜福利| 久久国产精品大桥未久av| 人妻制服诱惑在线中文字幕| 国产伦理片在线播放av一区| 日日摸夜夜添夜夜添av毛片| 女人久久www免费人成看片| 国产精品国产av在线观看| 国产在线视频一区二区| 国产毛片在线视频| 高清视频免费观看一区二区| 国产一区二区三区综合在线观看 | 日本91视频免费播放| 亚洲精品久久成人aⅴ小说 | 美女大奶头黄色视频| 草草在线视频免费看| 99久久综合免费| 99久久人妻综合| 国产精品一区二区在线观看99| 99热国产这里只有精品6| 91久久精品国产一区二区成人| 99热这里只有精品一区| 欧美三级亚洲精品| 丰满乱子伦码专区| 特大巨黑吊av在线直播| av有码第一页| 亚洲综合色网址| 精品一区二区三区视频在线| 国产不卡av网站在线观看| 亚洲激情五月婷婷啪啪| 久久精品久久精品一区二区三区| 国产日韩欧美亚洲二区| 日韩一本色道免费dvd| 男女国产视频网站| 18禁观看日本| 人妻夜夜爽99麻豆av| 久久人人爽人人爽人人片va| 国产日韩欧美视频二区| 性高湖久久久久久久久免费观看| 国产一区亚洲一区在线观看| 国产精品一二三区在线看| 99国产精品免费福利视频| 看非洲黑人一级黄片| av卡一久久| 久久精品国产鲁丝片午夜精品| 色网站视频免费| 十分钟在线观看高清视频www| 日韩免费高清中文字幕av| av在线老鸭窝| av在线观看视频网站免费| 美女xxoo啪啪120秒动态图| 国产69精品久久久久777片| 欧美日本中文国产一区发布| 各种免费的搞黄视频| 精品一区二区三区视频在线| 精品少妇黑人巨大在线播放| 久久精品久久久久久噜噜老黄| 777米奇影视久久| 女性被躁到高潮视频| 精品人妻在线不人妻| 久久99精品国语久久久| 午夜91福利影院| 天天影视国产精品| 91国产中文字幕| 久久 成人 亚洲| 新久久久久国产一级毛片| 欧美三级亚洲精品| 黄片播放在线免费| 日本91视频免费播放| 我的老师免费观看完整版| 国产亚洲午夜精品一区二区久久| 嘟嘟电影网在线观看| 中文欧美无线码| 亚洲欧洲国产日韩| 91久久精品国产一区二区成人| 卡戴珊不雅视频在线播放| 蜜桃久久精品国产亚洲av| 熟女av电影| 狠狠精品人妻久久久久久综合| 91精品一卡2卡3卡4卡| 男女免费视频国产| 国产成人精品婷婷| 狂野欧美白嫩少妇大欣赏| 国产精品不卡视频一区二区| 久久久久精品久久久久真实原创| 在现免费观看毛片| 午夜福利,免费看| 成人手机av| 久久精品久久精品一区二区三区| 熟妇人妻不卡中文字幕| 一级毛片黄色毛片免费观看视频| 国产亚洲午夜精品一区二区久久| 国产日韩欧美视频二区| 久久久久久久久久久免费av| 久久久国产一区二区| 国产精品嫩草影院av在线观看| 秋霞伦理黄片| 亚洲精品,欧美精品| xxxhd国产人妻xxx| 新久久久久国产一级毛片| 欧美三级亚洲精品| 美女xxoo啪啪120秒动态图| 嘟嘟电影网在线观看| 夫妻性生交免费视频一级片| √禁漫天堂资源中文www| 青春草国产在线视频| 五月开心婷婷网| av免费在线看不卡| 免费黄色在线免费观看| 久久久久久久久久久免费av| 国产精品欧美亚洲77777| 久久精品国产亚洲网站| 亚洲人成77777在线视频| 国产一区亚洲一区在线观看| 欧美丝袜亚洲另类| 国产精品久久久久久久电影| 久久ye,这里只有精品| 999精品在线视频| 亚洲av二区三区四区| 国产一区亚洲一区在线观看| 嘟嘟电影网在线观看| 精品国产露脸久久av麻豆| 日韩av免费高清视频| 麻豆精品久久久久久蜜桃| 欧美激情极品国产一区二区三区 | a级毛片黄视频| 考比视频在线观看| 人人妻人人澡人人看| 人妻人人澡人人爽人人| 国产不卡av网站在线观看| 哪个播放器可以免费观看大片| 精品国产国语对白av| 国产日韩欧美在线精品| 欧美日韩在线观看h| 热re99久久国产66热| 亚洲av成人精品一区久久| 男女边摸边吃奶| 精品少妇久久久久久888优播| 熟妇人妻不卡中文字幕| 亚洲精品视频女| 久久99热这里只频精品6学生| 国产在线一区二区三区精| 亚洲av日韩在线播放| 国产片内射在线| 91精品国产九色| 成人亚洲欧美一区二区av| 久久久国产一区二区| 日韩一区二区三区影片| 国产熟女欧美一区二区| 国产综合精华液| 国产深夜福利视频在线观看| 一区二区三区精品91| 在线观看免费高清a一片| 又黄又爽又刺激的免费视频.| 日韩av不卡免费在线播放| 日本爱情动作片www.在线观看| 97在线人人人人妻| 国产精品国产三级专区第一集| 亚洲,一卡二卡三卡| 丝袜喷水一区| 成人黄色视频免费在线看| 能在线免费看毛片的网站| h视频一区二区三区| 午夜av观看不卡| 性色avwww在线观看| 两个人免费观看高清视频| 一区在线观看完整版| av电影中文网址| 少妇的逼水好多| 国产精品秋霞免费鲁丝片| 亚洲精品日本国产第一区| 一本一本久久a久久精品综合妖精 国产伦在线观看视频一区 | 一本久久精品| 99re6热这里在线精品视频| 99热网站在线观看| 欧美成人精品欧美一级黄| 全区人妻精品视频| 日本av手机在线免费观看| 丝袜喷水一区| 日韩精品有码人妻一区| 99热6这里只有精品| 久久精品人人爽人人爽视色| 久久午夜综合久久蜜桃| 国产成人精品一,二区| 日本av免费视频播放| 性色avwww在线观看| 国产精品不卡视频一区二区| 中文精品一卡2卡3卡4更新| 人妻少妇偷人精品九色| 国产一区二区三区综合在线观看 | 久久国内精品自在自线图片| 亚洲国产日韩一区二区| 一级毛片电影观看| 国产亚洲av片在线观看秒播厂| 一区二区三区精品91| 午夜福利影视在线免费观看| 国产成人精品福利久久| 搡老乐熟女国产| 国产日韩欧美亚洲二区| 欧美bdsm另类| 人妻系列 视频| 国产av精品麻豆| 五月玫瑰六月丁香| 亚洲国产精品一区三区| 天美传媒精品一区二区| 插逼视频在线观看| 国产高清不卡午夜福利| 国产高清不卡午夜福利| 成人毛片60女人毛片免费| 男女边摸边吃奶| 18禁裸乳无遮挡动漫免费视频| 99久久中文字幕三级久久日本| 街头女战士在线观看网站| 汤姆久久久久久久影院中文字幕| 三级国产精品欧美在线观看| 久久久久久久久久久久大奶| 免费人妻精品一区二区三区视频| 视频区图区小说| 2018国产大陆天天弄谢| 国产亚洲欧美精品永久| 国产一区亚洲一区在线观看| 五月玫瑰六月丁香| a 毛片基地| av不卡在线播放| 少妇 在线观看| av不卡在线播放| 婷婷色av中文字幕| 国产高清三级在线| 哪个播放器可以免费观看大片| 久久久久精品性色| 夫妻性生交免费视频一级片| 中文字幕av电影在线播放| 一区二区日韩欧美中文字幕 | 91aial.com中文字幕在线观看| 久久国内精品自在自线图片| 色网站视频免费| 国产精品女同一区二区软件| 日韩一区二区视频免费看| 搡女人真爽免费视频火全软件| 午夜激情福利司机影院| 日本黄大片高清| 亚洲精品av麻豆狂野| 国产不卡av网站在线观看| 五月玫瑰六月丁香| av在线老鸭窝| 一级毛片 在线播放| 免费看av在线观看网站| 欧美日韩成人在线一区二区| 国产精品一区www在线观看| 久久久久久久久久人人人人人人| 免费观看性生交大片5| 国产精品国产av在线观看| 女人精品久久久久毛片| 久久久久久人妻| 街头女战士在线观看网站| 国产 精品1| 欧美日韩一区二区视频在线观看视频在线| 好男人视频免费观看在线| 国产毛片在线视频| 91久久精品国产一区二区三区| 久久久国产欧美日韩av| 亚洲国产av影院在线观看| 欧美丝袜亚洲另类| 在线观看免费日韩欧美大片 | 街头女战士在线观看网站| 精品人妻熟女av久视频| 人成视频在线观看免费观看| av不卡在线播放| 成人亚洲欧美一区二区av| 国产av国产精品国产| 蜜桃在线观看..| 欧美精品国产亚洲| 国产高清三级在线| 97超视频在线观看视频| av在线app专区| 视频区图区小说| 美女视频免费永久观看网站| 只有这里有精品99| 国产精品一二三区在线看| 国产成人精品无人区| 一区二区三区免费毛片| 成人免费观看视频高清| 久久97久久精品| 91精品一卡2卡3卡4卡| 欧美少妇被猛烈插入视频| 一级爰片在线观看| 久久人人爽人人爽人人片va| 日本欧美视频一区| 亚洲一级一片aⅴ在线观看| 久久精品国产亚洲av天美| 哪个播放器可以免费观看大片| 性色av一级| 亚洲一区二区三区欧美精品| 免费黄色在线免费观看| 欧美亚洲 丝袜 人妻 在线| 久久精品夜色国产| 男女边摸边吃奶| 黄色视频在线播放观看不卡| 人成视频在线观看免费观看| 日韩 亚洲 欧美在线| 高清黄色对白视频在线免费看| 久久国内精品自在自线图片| 我的老师免费观看完整版| 老司机影院成人| 国产精品久久久久久久电影| 国产精品嫩草影院av在线观看| 天堂中文最新版在线下载| 午夜老司机福利剧场| 久久久国产精品麻豆| 国产免费视频播放在线视频| 国产白丝娇喘喷水9色精品| 免费观看性生交大片5| 伊人久久精品亚洲午夜| 啦啦啦中文免费视频观看日本| 人妻一区二区av| 国产高清国产精品国产三级| 伦精品一区二区三区| 久久人人爽av亚洲精品天堂| 亚洲久久久国产精品| 成人漫画全彩无遮挡| 日韩成人伦理影院| 在线观看美女被高潮喷水网站| 麻豆成人av视频| 亚洲国产精品一区三区| 一个人看视频在线观看www免费| 亚洲国产精品一区三区| 国产成人freesex在线| 能在线免费看毛片的网站| 免费看光身美女| av国产精品久久久久影院| 亚洲在久久综合| 国产综合精华液| 亚洲人成网站在线观看播放| 看非洲黑人一级黄片| 免费高清在线观看视频在线观看| 欧美日韩视频精品一区| 免费观看的影片在线观看| 午夜视频国产福利| av福利片在线| 久久精品夜色国产| 久久女婷五月综合色啪小说| 各种免费的搞黄视频| 精品人妻熟女av久视频| 久久鲁丝午夜福利片| 久久久久久久久大av| 97精品久久久久久久久久精品| 国产成人freesex在线| 一级片'在线观看视频| 欧美成人精品欧美一级黄| 欧美老熟妇乱子伦牲交| 日韩制服骚丝袜av| 99热6这里只有精品| 不卡视频在线观看欧美| 日韩三级伦理在线观看| 香蕉精品网在线| 欧美日韩一区二区视频在线观看视频在线| 青青草视频在线视频观看| 精品人妻在线不人妻| av一本久久久久| 国产精品不卡视频一区二区| 久久精品久久精品一区二区三区| 夫妻性生交免费视频一级片| 免费日韩欧美在线观看| a级毛片在线看网站| 三级国产精品片| 国产黄频视频在线观看| 久久久久久久大尺度免费视频| 少妇被粗大猛烈的视频| 精品亚洲乱码少妇综合久久| 亚洲精品色激情综合| 免费少妇av软件| 2018国产大陆天天弄谢| 亚洲国产精品999| 国产成人av激情在线播放 | 免费观看a级毛片全部| 欧美日韩亚洲高清精品| 女人精品久久久久毛片| 亚洲精品久久成人aⅴ小说 | 免费人成在线观看视频色| 亚洲欧洲日产国产| 亚洲国产精品999| 亚洲精品av麻豆狂野| 亚洲成人av在线免费| 在现免费观看毛片| 蜜臀久久99精品久久宅男| 免费看av在线观看网站| 亚洲国产av影院在线观看| 又黄又爽又刺激的免费视频.| 一级a做视频免费观看| 午夜免费男女啪啪视频观看| 天美传媒精品一区二区| 国产乱来视频区| 黄片无遮挡物在线观看| 免费黄网站久久成人精品| 精品久久久久久电影网| 日本欧美视频一区| 国产日韩一区二区三区精品不卡 | 97在线视频观看| 国产精品不卡视频一区二区| 91精品国产国语对白视频| 国产精品久久久久久久电影| 久久精品夜色国产| 国产一区二区在线观看日韩| 精品亚洲成a人片在线观看| 亚洲国产欧美在线一区| 国产精品人妻久久久久久| 啦啦啦中文免费视频观看日本| .国产精品久久| 在线 av 中文字幕| 欧美日韩成人在线一区二区| 亚洲精品乱码久久久v下载方式| 各种免费的搞黄视频| 亚洲人成网站在线观看播放| 日日爽夜夜爽网站| 欧美xxⅹ黑人| 性色av一级| 精品国产一区二区久久| 在线观看一区二区三区激情| 国产亚洲午夜精品一区二区久久| 99re6热这里在线精品视频| 午夜福利视频精品| 永久免费av网站大全| 亚洲欧美日韩另类电影网站| 制服诱惑二区| 久久久a久久爽久久v久久| 欧美另类一区| 日韩,欧美,国产一区二区三区| 日韩欧美精品免费久久| 伊人亚洲综合成人网| 久久久精品区二区三区| 国产成人91sexporn| 欧美97在线视频| 搡老乐熟女国产| 国产白丝娇喘喷水9色精品| 日韩亚洲欧美综合| 亚洲精品久久久久久婷婷小说| 久久久久久久国产电影| 国产男人的电影天堂91| 久久久久久久久久成人| 夜夜骑夜夜射夜夜干| 国产永久视频网站| 精品99又大又爽又粗少妇毛片| 日韩大片免费观看网站| 亚洲人成网站在线观看播放| 久久韩国三级中文字幕| 三级国产精品欧美在线观看| 国产精品久久久久久精品古装| 99热网站在线观看| 国产不卡av网站在线观看| 男男h啪啪无遮挡| 男女免费视频国产| 亚洲精品456在线播放app| 女人精品久久久久毛片| 欧美老熟妇乱子伦牲交| 午夜老司机福利剧场| 亚洲一区二区三区欧美精品| 亚洲不卡免费看| 亚洲综合色网址| 亚洲国产精品999| 午夜91福利影院| 欧美精品人与动牲交sv欧美| 丝袜在线中文字幕| 777米奇影视久久| 日日摸夜夜添夜夜添av毛片| 精品久久久精品久久久| 亚洲av中文av极速乱| 高清毛片免费看| 男女边吃奶边做爰视频| 伦理电影大哥的女人| 久久久久精品性色| 26uuu在线亚洲综合色| 久久狼人影院| 日日摸夜夜添夜夜爱| 亚洲欧美一区二区三区黑人 | 在线 av 中文字幕| 观看av在线不卡| 国产一区有黄有色的免费视频| 黄片播放在线免费| 久久人妻熟女aⅴ| 成人二区视频| 中文精品一卡2卡3卡4更新| 一个人看视频在线观看www免费| 我要看黄色一级片免费的| 婷婷色麻豆天堂久久| 亚洲美女搞黄在线观看| 精品久久国产蜜桃| 久久久久久久久久久免费av| 欧美xxxx性猛交bbbb| 精品国产一区二区久久| 国产成人午夜福利电影在线观看| av国产久精品久网站免费入址| 18在线观看网站| 亚洲精品一区蜜桃| 搡老乐熟女国产| 九九在线视频观看精品| 久久精品国产亚洲网站| 国产精品国产三级国产av玫瑰| 人妻一区二区av| av不卡在线播放| 成人黄色视频免费在线看| 黄色欧美视频在线观看| 免费观看无遮挡的男女| 一级,二级,三级黄色视频| 99久久人妻综合| 男女高潮啪啪啪动态图| 国产av精品麻豆| 天堂俺去俺来也www色官网| 一级毛片 在线播放| 伦精品一区二区三区| 一本一本综合久久| 成人黄色视频免费在线看| 中文字幕久久专区| 在线观看免费高清a一片| 男女边摸边吃奶| 国产日韩欧美亚洲二区| 青青草视频在线视频观看| 大话2 男鬼变身卡| 午夜精品国产一区二区电影| 一边亲一边摸免费视频| 国产成人精品在线电影| 午夜激情福利司机影院| 亚洲一级一片aⅴ在线观看| 十八禁网站网址无遮挡| 国产精品嫩草影院av在线观看| 欧美bdsm另类| 午夜免费男女啪啪视频观看| 亚洲精品国产av成人精品| 久久99蜜桃精品久久| tube8黄色片| 欧美日韩视频高清一区二区三区二| 免费观看在线日韩| 999精品在线视频| 亚洲av福利一区| 日日撸夜夜添| 久久这里有精品视频免费| 免费大片18禁| 国产欧美亚洲国产| av国产久精品久网站免费入址| 免费观看av网站的网址| 久久国内精品自在自线图片| 欧美精品一区二区大全| 热re99久久精品国产66热6| 视频区图区小说| 亚洲欧美成人精品一区二区| 亚洲av免费高清在线观看| 日本午夜av视频| av视频免费观看在线观看| 99九九在线精品视频| 亚洲色图 男人天堂 中文字幕 | 亚洲,欧美,日韩| 男人爽女人下面视频在线观看| 九九久久精品国产亚洲av麻豆| 日韩在线高清观看一区二区三区| av不卡在线播放| 亚洲欧洲国产日韩| 色5月婷婷丁香|