Scientists have always wanted to know more about the universe. Years ago they knew many things about the moon. They knew how big

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问题     Scientists have always wanted to know more about the universe. Years ago they knew many things about the moon. They knew how big it was and how far away from the earth. But they wanted to know more about it. They thought the best way was to send men to the moon. The moon is about 384, 000 kilometers away from the earth. A plane cannot fly to the moon because the air reaches only 240 kilometers away from the earth. But something can fly even when there is no air. That is a rocket.
    How does a rocket fly? There is gas in the rocket. When the gas is made very hot inside the rocket, it will rush out of the end of the rocket, so it can make the rocket fly up into the sky. Rockets can fly out into space. Rockets with men in them have been to the moon. Several rockets without men in them have flown to another planet much farther away than the moon. One day rockets may be able to go to any place in space.  
The hot gas in the rocket is used for______.

选项 A、keeping the air in the rocket fresh
B、keeping the men in the rocket warm
C、making the rocket fly up
D、cooking food for the men

答案C

解析 事实细节题。由第二段第三句“When the gas is made very hot…so it can make the rocket fly up intothe sky.”可知,火箭内的热气可以使火箭向上飞行。故选C。
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