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. While we are asleep our bodies grow most. Children who are tired usually
need more sleep. We can get our lessons better and we feel better too, when we 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 (新鲜的) air we'll feel tired when we wake up. While
 in bed we must not cover our heads. If we do, our lungs (肺) will not 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 grow and be strong must get plenty of sleep.

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