阅读理解。

     In the day we work and play, at night we sleep. Our body rests while we sleep. In the morning we are

ready to work and play again. Our body grows most while we are asleep.

     Most Americans sleep an average (平均) of seven to eight hours a night. Some people need only three

or four hours of sleep a night. Children usually need more sleep. We can study our lessons better after we

have lots of rest. Boys and girls need ten hours of sleep every night when they are eight or nine years old.

After age fifty, the average sleep time goes down to 6.5 hours a night.

     Our body needs lots of air when we sleep. If we do not get enough fresh (新鲜的) air,we will feel tired

when we wake up. While in bed we must not cover our head. Our lung (肺) needs to get enough fresh air.

If we open our windows at night,we can have plenty of fresh air. Cool air is better than warm air. Boys and

girls who want to be strong must get plenty of sleep.

1. The world "cover" in the passage means ________.

A. 遮盖

B. 包含

C. 封面

D. 顶替

2. How many hours of sleep should a nine-year-old child have?

A.6.5 hours.

B. 7 hours.

C. 8 hours.

D. 10 hours.

3. What does the lung need most?

A. Fresh air.

B. Covering.

C. Warm air.

D. Exercise