Directions: Complete the following passages by using the words in the box. Each word can only be used once. Note that there is one word more than you need.

A. struggling            B.suit               C. produce            D. extension       E. treat F. performance     G. suggests     H. recover          I. force            J. reset       K. flowing

Walking through any high school during the first class in the morning, you may find that many students are 【小题1】 to keep their heads up. “They’re sitting in the classroom, but their heads are at home on their pillows,” says Mary Carskadon of Brown Medical School in the US.

Don’t blame yourself; blame the clock in your brain. Two decades of research 【小题2】 that your bodies are pushing you to stay up at night and sleep into the morning. During the first several weeks of school, students are more likely to get a(n) lack of sleep. In the holidays, most students can sleep over eight hours a night. But during the school day, students on average sleep only about six hours. Students will lose 10 hours of sleep per week that they never 【小题3】 from. The lack of sleep may not only be a drag (拖后) on school 【小题4】, but also be related to poor health.

Scientists in the US led research to try to 【小题5】 teenagers’ clocks back to help them fall asleep earlier. They use a special light in the classroom to try to 【小题6】 a reset of the students’ biological clock. They found the brain can 【小题7】 a chemical that helps sleep. It comes out only in the dark. The research failed at the end. Doctor said that even if the chemical had started 【小题8】, the kids’ homework and other activities meant they stayed up at night.

Some schools have reset their school time from 7:25 to 8:30 a.m. to 【小题9】 the students. The results were so encouraging that students who had the hour 【小题10】of sleep performed best in tests. Those who lost the hour did worst of all.