2. 外语
  3. If the population of the Earth goes on increasing at its present rate, there will【B1】______ not be enough resources left to【B2】_

If the population of the Earth goes on increasing at its present rate, there will【B1】______ not be enough resources left to【B2】_

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问题     If the population of the Earth goes on increasing at its present rate, there will【B1】______ not be enough resources left to【B2】______ life on the planet. By the middle of the 21st century, if present【B3】______continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of【B4】______the human race, the【B5】______ 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【B6】______, it will be possible to change the【B7】______ 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【B8】______amount of water there.
    【B9】______. As soon as this has been done, the algae will be placed in small rockets.【B10】______. 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 can set foot on Venus, it will be necessary for the oxygen to produce rain.【B11】______
【B2】
选项
答案sustain
解析 此处需要一个原形及物动词，sustain是四六级核心词汇，此处表示“供给必需品及营养”。
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