During the day we work and play，and at night we sleep. Our body rests when we sleep. In the morning we are ready to work and play again. Our body grows most when we are asleep. Children who are tired usually need sleep. We can get better at our lessons after having plenty of rest. Boys and girls who are 8 or 9 years old need 10 hours of sleep every night. Our body needs plenty of air when we are asleep. If we do not get enough fresh air, we will feel tired when we wake up. While in bed we must not cover our head，our lungs need 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.（plenty of: 大量的、充足的）
阅读上面短文，选出正确的答案。
Our body grows most when we are _______.
A. eating    B. playingC. sleeping
How many hours of sleep should 9-year-old children have every night?
A. 8 hours.B. 9 hours.C. 10 hours.
If we don’t get enough fresh air, we will feel _______.
A. tiredB. hungryC. happy   \
What do the lungs need most?
A. Warm air.B. Exercise.C. Fresh air.
Which kind of air is better when we sleep?
A. cool air B. Warm air  C. both A and B