根据下列短文内容，在短文后的空格处填上一个恰当的词，使短文完整、通顺。
During the day we work and play. At night we sleep. Our body rests and grows most while we 78 asleep. 79 the morning we are ready to work and play again. Children who are tired usually need more sleep. We can study better after we have 80 rest. Boys and girls who are eight or nine years old 81 ten hours of sleep every night.
Our body needs fresh air when we sleep. 82 we do not get enough fresh air, we will feel tired when we wake up. We should 83 our windows at night, and we can have a lot of fresh air. Cool air is better 84 warm air. Boys and girls who want to be 85 must get pleny of sleep.