The rockets take astronauts and man-made satellites into space. The satellites are used for munication, weather monitoring and research. But how do satellites stay up without falling down?
There are two opposite forces (力量) acting on the satellite. One of them is the force of gravitation (地心引力), which tries to pull the satellite towards the earth. The other force is created by the rotation (旋转) of the satellite around the earth. This force tries to take the satellite away from the earth. With these two forces, the satellite goes round and round. The gravitational pull of the earth (the force which pulls everything towards the ground) is like a rope which keeps the satellite from flying away.
Everything that goes up has to e down. It is only a matter of time before a satellite es back to the earth. As time goes by, the satellite loses its speed, which makes the gravitational pull stronger than the force pulling it away. This makes the satellite crash (坠落) down to the earth.
【小题1】Which of the following uses of satellites is NOT mentioned?A．municationB．monitoring the weather conditionC．doing some researchD．taking pictures【小题2】The force that pulls the satellite towards the earth is created by .A．the earth B．the satellite itselfC．the rotation of the satelliteD．the rope【小题3】Why can’t the satellites fly away?A．Because of the force from the earth.B．Because the satellite is too big.C．Because of the force created by the rotation of the satellite around the earth.D．Because people on earth have made ropes to tie the satellites tightly.【小题4】The satellite will finally crashes down to the earth .A．when it flies fasterB．when its speed slows downC．when people cut the ropeD．when there is no electricity in it【小题5】Which of the following is TRUE according to the passage?A．There are four forces acting on the satellite.B．The force of gravitation makes the satellite go round and round.C．As time goes by, the satellite will finally fall down.D．The satellite will stay in space forever.D
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(答案→)D
解析：短文属于说明文。介绍了人造卫星不会坠落的原理。
【小题1】细节理解题。从第一段第二句“…are used for munication, weather monitoring and research.”可知没提到D项。
【小题2】推理判断题。从第二段最后一句“The gravitational pull of the earth”可知地心引力来自于地球。
【小题3】综合理解题。从第二段第二句“…tries to pull the satellite towards the earth”和最后一句“…keeps the satellite from flying away”可知：是因为地心引力。
【小题4】细节理解题。从短文后两句“…loses its speed…crash down to the earth”可知。
【小题5】综合理解题。通读全文，可知A、B、D三项不符合文意；C项与短文最后一段吻合。