For thousands of millions of years the moon has been going round the earth.At that time，the moon was the __1__ satellite(卫星)of the earth.Today，__2__，the earth has many other satellites.All of them are __3__ by man.These man­made satellites are very much smaller than the moon.However，some of them will still be going __4__ the earth thousands of years from now.

　　Man­made satellites don't __5__ because they are going too fast to do so.As they speed along，they __6__ to go straight off into space.They __7__ out of the earth，or its gravity，which __8__ them from doing this.As a result，they travel in an orbit(轨道)round the earth.

　　If a man­made satellite travels about at a certain height，it can keep going __9__ round the earth，just like the moon.This is __10__ it is above the atmosphere(大气)，and there is nothing to __11__ it down.If it travels __12__ than that，it will be slowed down so much that it will __13__ the earth.

　　Men have __14__ spaceships to the moon and to the two __15__ planets Mars(火星) and Venus(金星).By putting a camera on __16__ the spaceship to the moon，men have been able to __17__ photographs of the other side of the moon.This side is always __18__ from us as the moon __19__ the earth.The __20__ were later transmitted by radio to the earth.They showed that the other side of the moon is very much the same as the side that turns towards us.

　　1.A.first B.second

　　C.last D.only

　　答案：D　从常识以及下文的many other satellites可知在人造卫星之前月亮是地球唯一(only)的卫星。

　　2.A.then B.however

　　C.though D.so

　　答案：B　前后两句间有转折关系，所以用副词however“然而”。

　　3.A.found B.discovered

　　C.made D.sent

　　答案：C　根据下文These man­made satellites可知这些卫星是人造卫星。

　　4.A.with B.round

　　C.behind D.after

　　答案：B　根据上文going round the earth可知这些卫星绕着地球转。

　　5.A.fall B.rise

　　C.break D.stop

　　答案：A　根据下文的they travel in an orbit round the earth.可知这些人造卫星由于速度快所以不会掉(fall)下来。

　　6.A.want B.wish

　　C.hope D.tend

　　答案：D　当加速时，卫星易于(tend to)进入太空。

　　7.A.pull B.push

　　C.take D.launch

　　答案：A　卫星离开(pull out of)地球，进入轨道。

　　8.A.protects B.keeps

　　C.makes D.discourages

　　答案：B　地球重力阻止卫星离开地球。keep...from doing...“阻止……做某事”。

　　9.A.in and in B.on and on

　　C.out and out D.up and up

　　答案：B　从上文可知卫星会一直绕着地球转。on and on“不停地”。

　　10.A.because B.why

　　C.whether D.when

　　答案：A　本句介绍前句的原因。This is because...“这是因为……”。

　　11.A.hand B.force

　　C.slow D.bring

　　答案：C　根据上下文可知大气会使卫星慢下来。slow sth.down“使……慢下来”。

　　12.A.higher B.longer

　　C.more D.lower

　　答案：D　与上文above the atmosphere构成对应，所以使用lower。

　　13.A.leave away B.fall to

　　C.go after D.knock over

　　答案：B　根据第二段第一句可知如果它的速度慢下来，卫星会掉入(fall to)地球。

　　14.A.gave B.offered

　　C.sent D.drove

　　答案：C　人们已经把宇宙飞船送上(send)了月球。

　　15.A.nearest B.smallest

　　C.biggest D.closest

　　答案：A　由常识可知Mars(火星)and Venus(金星)是最近的(nearest)两个星球。closest表示“最靠近的”。

　　16.A.board B.right

　　C.left D.top

　　答案：A　board the spaceship“在宇宙飞船上”。

　　17.A.form B.film

　　C.catch D.take

　　答案：D　take photographs of“拍照”。

　　18.A.far B.hidden

　　C.different D.separated

　　答案：B　根据下文可知the other side of the moon是月球背朝地球的那一面。

　　19.A.leads B.obeys

　　C.circles D.pursues

　　答案：C　月球围绕(circle)地球转。

　　20.A.information B.letters

　　C.sounds D.photos

　　答案：D　根据上文提到的photographs可知将照片(photos)发回地球