During the day we work and play. At night we sleep. Our bodies rest while we sleep. In the morning we are ready to work and play again. Our bodies grow most while we are asleep. Children usually need more sleep than adults. They can learn their lessons better after they have had plenty of rest. Boys and girls who are eight or nine years old need ten hours of sleep every night. Our bodies need plenty of air when we sleep. If we do not get enough fresh air, we will feel tired when we wake up. While in bed we must not cover our heads. Our lungs（肺）need to get enough fresh air. If we keep our windows open at night, we can have plenty of fresh air in the room.

1. Our bodies grow most while we are ________________.

A. eating B. playing C. sleeping D. exercising

2. Too little sleep makes us ________.

A. tired B. hungry C. happy D. grow

3. What may cause us to feel tired in the morning?

A. Too much air. B. Not enough fresh air.

C. Too much cold air. D. Too much sleep.

4. How many hours of sleep should 9-year-old children have every night?

A. Eight hours. B. Nine hours.

C. Ten hours. D. Eleven hours