第4部分：阅读理解(第31～45题，每题3分，共45分)
下面有3篇短文，每篇短文后有5道题，每题后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题，从4个选项中选择1个最佳答案涂在答题卡相应的位置上。
第一篇 A Thirsty World
The world is not only hungry,it is also thirsty for water．This may seem strange to you，since nearly 75％of the earth's surface is covered with water．But about 97％of this huge amount is sea．water,or salt water．Man can only drink and use the other 3％一the fresh water that comes from rivers，lakes，underground，and other sources．And we cannot even use all of that，because some of it is in the form of icebergs(冰山)and glaciers(冰川)．Even worse，some of it has been polluted．
At the moment，this small amount of flesh water is still enough for us：However，our need for water is increasing rapidly．Only if we take steps to deal with this problem now can we avoid a severe worldwide water shortage later on．A limited water supply would have a bad effect on agriculture and industry．
In addition to stopping wasting our precious water,one useful step we should take is to develop ways of reusing it．Experiments have already been done in this field，but only on a small scale．
Today,in most large cities．water is used only once and it eventually returns to the sea or runs into underground storage tanks．But it is possible to pipe water that has been used to a purifying(净化)plant．There it can be filtered(过滤)and treated with chemicals so that it can be used again just as if it were fresh from a spring．
But even if every large city purified and reused its water,we still would not have enough．Where could we turn next?To the oceans!A11 we'd have to do to make use of the vast amount of sea．water is-remove the salt．This salt．removing process is already in use in many parts of the world．
So if we take all these steps，we'11 be in no danger of drying up!
31 The phrase "the world"in the first line of the passage refers to
A "man"．
B "you"．
C "woman"．
D "they"．
32 What percentage of the earth's water can mall actually use at present?
A Nearly 75 per cent．
B About 97 per cent．
C Exactly 3 per cent．
D Lessthan 3 per cent．
33 According to the passage，we can avoid a worldwide water shortage in the future by
A increasing rainfall．
B reusing water and utilizing sea-water．
C cutting down our consumption of water．
D reducing the number of factories producing steel．
34 Which of the following statements，according to the passage，is NOT true?
A A limited water supply will affect industrial production．
B Every large city purifies and reuses its water．
C Purified water is not exactly as fresh as spring water．
D Oceans are the largest water source．
35 According to the passage，sea-water can be turned into fresh water by
A heating it up．
B treating it with chemicals．
C taking salt out of it．
D drying it up．
第二篇 Life in the Universe
Many scientists today are convinced that 1ire exists elsewhere in the universe-life probably much like that on our own planet．They reason in the following way．
As far as astronomers(天文学家)can determine，the entire universe is built of the same matter．They have no reason to doubt that matter obeys the same laws in every part of the universe；Therefore，it is reasonable to guess that other stars，with their own planets，were bom in， the salne way as our own solar system．What we know of lire on earth suggests that life will arise wherever the proper conditions exist．
Life requires the right amount and kind of atmosphere．This eliminates all those planets ill the universe that are not about the same size and weight as the earth．A smaller planet would lose its atmosphere；a larger one would hold too much of it．
Life also requires a steady supply of heat and light．This eliminates double stars．or stars that flare up(闪耀)suddenly．Only single stars that are steady sources of heat and light like our sun would qualify．
Finally,life could evolve only if the planet is iust the right distance from its sun．With a weaker sun than our own，the planet would have to be closer to it．With a stronger sun，it would have to be farther away．
If we suppose that every star in the universe has a family of planets，then how many planets might support life?First，eliminate those stars that are not 1ike our sun．Next，eliminate most of their planets；they are either too far from or too close to their suns．Ttmn eliminate all those planets which are not the same size and weight as the earth．Finally,remember that the proper conditions do not necessarily mean that life actually does exist on a planet．It may not have begun yet，or it may have already died out．
This process of elimination seems to leave very few planets on which earthlike life might be found．However,even if life could exist on only one planet in a million．there are so many billions of planets that this would stillIeave a vast number on which life could exist．
36 Astronomers belmve that matter in different parts of the universe
A obeys different laws．
B obeys one common law．
C obeys the same laws．
D obeys no common law．
37 The passage mentions all of the following factors for the existence of life EXCEPT
A the fight amount of atmosphere．
B a steady supply of water．
C steady heat and light．
D the fight distance from the sun．
38 Which of the following statements is INCORRECT?
A Astronomers believe that the universe is built of the same matter．
B Proper conditions are essential to the existence of life．
C Double stars can provide steady light and heat．
D Astronomers believe that other solar systems are similar in structure to ours．
39 What kind of planet elsewhere in the universe can support life?
A Those double stars'planets．
B Those planets much hotter than our earth．
C Those planets similar to the earth．
D Those planets very close to their suns．
40 At the end of the passage the author suggests that
A it is impossible for life to exist on other planets
B earthlike life could only exist on a few planets．
C life could exist on only one planet in a million．
D life could exist on a great number of planets．
