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Everyone knows we can’t live a happy life without good health. As for students, we can’t study well if we don’t have enough sleep. Sleep is important to everyone as well as students. However,         start before 8:00am, which means that most students have to wake up at about 6:30am. This makes           almost impossible for teenagers to sleep for nine hours that the National Sleep Foundation(NSF, 国家爱睡眠基金会) suggested. Students’ health condition and their grades would          if teenagers could sleep for as long as the suggested number of hours.
   to the NSF, it is normal for teenagers to go to bed late. Only about 15% of teenagers fall asleep        10:45pm, about 5%go to bed about 10:45, and about 80% go to bed after 11:00pm. Many teenagers have sleeping problems.
What’s more, doctors say that lack(缺少) of sleep is the top health problem. If it is true, why can’t something be         to help students get more sleep? Studies show that teenagers who sleep for nine and a half hours are late for class less often and have         health problems.
Another benefit(益处) of starting classes later is that students’ grades would improve. Enough sleep helps students pay more attention to           their teachers say. And then they can have more chances to get better grades.
It is really important for teenagers to get enough sleep so that they may stay healthy and get good grades. To let students make it, classes do need to begin later.