阅读理解，请根据短文回答其后面的问题，为每题确定一个最佳答案。

　　Rockets in the Sky

　　If someone asked you．"What color is the sky?"I expect that you would answer，"Blue．"I amafraid that you would be wrong．The sky has no color．When we see blue，we are looking at bluesunlight．The sunlight is shining on little bits of dust in the air．

　　We know that there is air all around the world．We could not breathe without air．Airplanescoutd not fly without air．They need air to lift their wings．Airplanes cannot fly very high because asthey go higher the air gets thinner．If we go far enough away from the earth，we find there is no air. What is the sky?The sky is space．In this space there is nothing except the sun，the moon andall the stars．

　　Scientists have always wanted to know more about the other worlds in the space．They havelooked at them through telescopes and in this way they have found out a great deal．

　　The moon is about 384．000 kilometers away from the earth．An airplane cannot fly to the moonbut there is a thing that can fly even when there is no air．This is rocket．

　　I am sure that you are asking．"How does a rocket fly?"If you want to know，get a balloon andthen blow it up until it is quite big．Do not tie up the neck of the balloon．Let go!The balloon willfly off through the air very quickly．The air inside the balloon tries to get out．It rushes out through neck 0f the ballOOfl and this pushes the balloon through the air．It does not need wings like an air. plane．

　　This is how a rocket works．It is not made of rubber like a balloon，of course．It is made ofmetal．The metal must not be heavy but it must be very strong．There is gas inside the rocket whichis made very hot．When it rushes out of the end of the rocket，the rocket is pushed up into the air．

　　Rockets can fly far out into space．Rockets with men inside them have already reached themoon．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 the space．

　　41．What color is the sky?

　　A．It iS blue． B．It iS white．

　　C．It is grey．D．It has no color．

　　42．When an airplane flies too high，___________.

　　A．the air will be too thin to support its wings．

　　B．the air will become thicker．

　　C．the air will exert pressure on it．

　　D．the air will disappear in no time．

　　4 3．A rocket can fly to the moon because__________

　　A．it looks like a balloon．

　　B．it is much lighter than an airplane．

　　C．it doesn't have wings．

　　D．it works like an untied balloon．

　　44．Which of the following statements about a rocket is NOT true?

　　A．It can fly when there is no air．

　　B．It can fly without wings．

　　C．It is made of strong metal．

　　D．It is propelled by burning gas inside it．

　　45．A rocket is pushed up into the air when__________

　　A．hot gas rushes out of its head．

　　B．it is powered by gas．

　　C．hot gas rushes out of its bottom．

　　D．hot gas rushes out of its neck．

　　参考答案及解析

　　41．D [解析]文章第一段第三句"The sky}las no color．"

　　42．A [解析]文章第二段第三句"Airplanes cannot fly very high beeause as they go higherthe air gets thinner．"

　　43．D [解析]文章第六段都在综述气球的飞行原理，来解释火箭的工作原理，因此选D。

　　44．D[解析]文章中第七段倒数第二句"There is gas inside the rocket which is macle veryhot．"但并没有说明是burning，所以不对。

　　45．C[解析]文章倒数第二段的最后一句话"Wllen it rushes out ofthe end of the rocket．"

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