Though times have changed， falling asleep in class is still a common occurrence（常事）among teenagers．

    Why do students sometimes fall asleep in class？ An obvious reason is lack of sleep． However， there are also causes for getting too little sleep．

Homework is a daily occurrence for most students， one that can take three

to four hours per night． A teenager who wants to be able to take part in

any activity besides homework must stay up late to fit everything in． Club

activities， sports， computer﹣game playing， and TV viewing，for example，all contribute to （促成） teens having less time for both homework and sleep．Sometimes teens lack sleep because of after﹣school jobs that are taken on to earn extra money for college， family expenses， or simply for clothes．

    Physical problems are another factor that can cause students to fall alseep in class． For example，

insomnia， which may keep a student up at night， causing exhaustion（疲惫不堪）during class hours，

is a serious problem that may require medical attention． Medical evidence also supports the idea that each person has a body clock that helps to decide his or her sleep pattern． Unluckily， these body clocks do not always work according to school timetables．

    The effects of falling asleep in class can be quite serious． First of all， sleeping in class is not a good way to endear（使受喜爱） yourself to teachers． In addition， it is highly possible that other students may make jokes about those who sleep in class． However， the most harmful effect of sleeping in class is missing out on important points． In the long run， sleepers may end up failing classes．

    Since teens are probably not going to deal with the problem， falling asleep in class will probably remain an all﹣too﹣common occurrence． It will continue until more teens find a way to balance their personal and social lives with school and work， while still finding enough time to sleep．

Introduction	Times have changed，（1）　　falling asleep in class is still quite common．
Causes	Lack of sleep ◆To （2）　　doing their homework， students may have to work three to four hours every night． ◆To （3）　　homework with activities， students may stay up late． ◆To spare time for after﹣school jobs， students may not have （4）　　time to sleep． Physical problems ◆Insomnia may （5）　　students falling asleep at night． ◆Students' body clocks do not always （6）　　their school timetables．
Effects	◆Students sleeping in class may not be （7）　　by their teachers． ◆Students who sleep in class run the （8）　　of being laughed at． ◆Students who sleep too much in class may miss out on important knowledge and （9）　　in their study．
Conclusion	The problem will not be （10）　　until teenagers can manage their lives， deal with their school and work， and then still have time to sleep．