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  3. If the population of the Earth goes on increasing at its present rate, there

If the population of the Earth goes on increasing at its present rate, there

游客2025-03-25  20
问题     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 21 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 proposed that algae, organisms that 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 carbon dioxide into oxygen and carbon.
    When the algae have done their works, 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 something like Earth will be reproduced on Venus.
    If the experiments are successful, life will become possible there, but it will not be pleasant at first. When they go to Venus, the first colonists will have to take plenty of water with them and get used to days and nights lasting 60 Earth-days. But there will also be some advantages. The colonists will live longer because their hearts will suffer less strain than on Earth. Apart from that, they will be exploiting a new world while those still on Earth are living in closed, uncomfortable conditions. Perhaps it will be the only way to ensure the survival of the human race. [br] Algae are important for the colonization of Venus since ______.
选项 A、they can be bred in any conditions
B、they produce oxygen
C、they can easily be carried in spaceship
D、they can make the carbon dioxide in a fairly short time
答案 B
解析 本题是细节题。文中第三段讲Sagan proposed that algae，organisms that 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. 海藻能够在极热或极冷的气候下生存，并且能够产生氧气，而据文章第三段讲：金星上没有氧气，且气候异常，因此将海藻植于金星是非常重要的开发手段，所以B选项是正确答案。A选项根据常识可以排除，C选项不是理由，试想仅能轻易携带而于开发无益的东西有什么用呢? D选项与文章内容不符，海藻不产生二氧化碳。
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