单选题 If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the car- bon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years some- thing like earth will be reproduced on Venus.

单选题 In the long run, the most difficult problem caused by population growth on earth will probably be the lack of ______.

A. food
B. oil
C. space
D. resources

【正确答案】 C

【答案解析】[解析] 由第一段可知，如果人口按照目前速度持续膨胀的话，地球上最终会缺乏资源来维持这么多的生命。即使科学家发明出替代资源，拥挤的人口也使我们不得不到其他星球寻找生存空间。但是目前太阳系还没有发现能维持生命的行星。因此和缺乏资源相比，缺乏生存空间才是最令人担忧、最难解决的问题。所以正确答案为C。

单选题 Carl Sagan believes that Venus might be colonized from earth because ______.

A. it might be possible to change its atmosphere
B. its atmosphere is the same as the earth's
C. there is a good supply of water on Venus
D. the days on Venus are long enough

单选题 On Venus there is a lot of ______.

A. water
B. carbon dioxide
C. carbon monoxide
D. oxygen

【正确答案】 B

【答案解析】[解析] 由第二段的最后一句话中的“there is only a tiny amount of water there (Venus)”得知，A选项错误。第三段结尾说明，藻类通过火箭运往金星，然后“In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon”，说明金星上有大量的二氧化碳。C和D选项错误。故选B。