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 eight or nine years old need ten 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(覆盖) 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.
Our body grows most while we are _______.
A.eating    B.playing   C.sleeping 
Too little sleep makes us _______.
A.tired B.hungry    C.happy
—What may cause us to feel tired in the morning?
—_______ during the sleep.
A.Too much air      B.Not enough fresh air
C.Too much cold air    
How many hours of sleep should 9-year-old children have every night?
A.8 hours.  B.9 hours.  C.10 hours.
What do the lungs need most?
A.Fresh air.    B. Exercise.    C.Warm air.