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  3. If the population of the Earth goes on increasing at its present rate, there will eventually not be enough resources left to【B1】

If the population of the Earth goes on increasing at its present rate, there will eventually not be enough resources left to【B1】

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问题     If the population of the Earth goes on increasing at its present rate, there will eventually not be enough resources left to【B1】______ life on the planet. By the middle of the 21st century, if present【B2】______ 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 【B3】______ conditions on Earth will make it necessary for us to look for open space somewhere else.
    An American scientist, Professor Carl Sagan, believes that before the earth’s resources are completely【B4】______, 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【B5】______ that algae(藻类), organism that can live in 【B6】______ hot or cold atmospheres and at the same time produce oxygen, should be【B7】______ 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【B8】______ the carbon 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【B9】______ of the planet will still be too hot for men to【B10】______ it but the rain will eventually fall and in a few years something like Earth will be reproduced on Venus.
【B4】
选项
答案exhausted
解析 根据空格前的系动词are，推断此处用过去分词表被动。注意exhaust“耗尽”不要漏掉字母h。
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