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

游客2025-03-06 40

问题 If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to keep our lives 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. 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 American scientist, Professor Carl Sagan.
Sagan believes that before the earth’s resources are completely used up 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(藻类)organisms that can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in condition similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceship 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 work, the atmosphere will become cooler, but before man ban 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 man to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus. [br] Man can land on Venus only when______.

选项 A、the algae have done their work
B、the atmosphere becomes cooler
C、there is oxygen
D、it rains there

答案 B

解析此题问的是人类在什么情况下可以登上金星，属于细节事实题，正确答案可以在最后一段中找到。此段讲到了“当藻类植物发挥作用之后，大气层会冷却，但是在人类登陆之前，氧气要能够产生雨水，因为金星表面对于人类来说仍然过热，但是雨水降下后的几年，金星的整个环境就会变得与地球类似，所以可以推断人类只有在大气层冷却之后才能登上金星”。正确答案选择B。

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