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阅读理解
Scientists have always wanted to know more about the other worlds in space．They have looked at them through telescopes(望远镜)and in this way they have found out a great deal．They know many facts about the moon．For example, they know how big it is and how far away．But they wanted to know more about it．The only way to find out more was to send men to the moon．Then they would know all about it．
The moon is about 184,000 kilometers away from the earth．An airplane cannot fly to the moon because the air reaches only 240 kilometers．Then there is no air．But there is something that can fly even when there is no air．There is a rocket．
I am sure that you are asking, “How does a rocket fly?”If you want to know, get a balloon and then blow it up, until it is quite big．Do tie up the neck of the balloon, let it go．The balloon will fly off through the air very quickly．The air inside the balloon tries to get out．It rushes out through the neck of the balloon and this pushes the balloon through the air．It does not need wings(翅膀)like a plane．
This is how a rocket works．It is not made of rubber(橡胶)like a balloon, of course．It is made of metal(金属)．The metal must not be heavy but it must be very strong, there is gas inside the rocket, which is made very hot．When it rushes out of the end of the rocket, the rocket is pushed up into the air．
Rockets can fly out into space．Rockets with men inside them have already reached the moon．Several rockets without men inside them have been sent to other worlds much farther away．One day rockets may be able to go anywhere in space．
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