“历史时期”是历史学的基本概念.阅读“我国1919年以来主要历史时期年代尺”，回答问题.

    During the day we work and play, and at night we sleep. Our bodies rest while we are 1. In the morning we are ready2 again. Our bodies grow 3 while we are asleep. Children who are tired usually 4 sleep. We can get better at our lessons 5 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 6 when we sleep. If we do not get enough fresh air, we 7 tired when we wake up. While in bed we must not cover our 8. Our lungs(肺) need to get enough fresh air. If we 9 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 10 must get plenty of sleep.

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    Tom is a young man. He eats and sleeps a lot, 1 works a little. He doesn't like to learn, so he2little. He can't do any difficult work, so he has to look 3an easy job. One day he finds a job on a farm. When it's work time, he always says he's tired and 4. So he gets less money than the others. 5 is coming. The workers are getting ready for the next year. Only Tom does 6. The farmer tells him to cut down trees in the forest. The young man goes there with a 7. He feels terrible in the forest and 8 about the animals. So he looks around and sings loudly. Nobody knows 9 he's singing.

    After three days, Tom hasn't cut down any trees. The farmer wants to find out how the young man is doing. He's 10 when he finds Tom sitting on the chair, cutting the tree. “Why are you sitting here to cut the tree?” asks the farmer. “Because I can't work if I am lying(躺)down, sir.”