With the world’ s population estimated to grow from six to nine billion by 2050, researchers, businesses and governments are alr

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问题    With the world’ s population estimated to grow from six to nine billion by 2050, researchers, businesses and governments are already dealing with the impact, this increase will have on everything from food and water to infrastructure and jobs. Underling all this【C6】______will be the demand for energy, which is expected to double over the next 40 years.
   Finding the resources to meet this demand in a【C7】______, sustainable way is the cornerstone of our nation’ s energy security, and will be one of the major【C8】______of the 21st century. Alternative forms of energy-bio-fuels, wind and solar, to name a few are【C9】______being funded and developed, and will play a growing【C10】______in the world’ s energy supply. But experts say that even when【C11】______, alternative energy sources will likely meet only about 30% of the world’ s energy needs by 2050.
   For example, even with【C12】______investments, such as the $ 93 million for wind energy development【C13】______in the American Recovery and Reinvestment Act, important alternative energy sources such as wind and bio-fuels【C14】______only about 1 % of the market today.
   Energy and sustainability experts say the answer to our future energy needs will likely come from a lot of【C15】______both traditional and alternative.
   [A]consist[B]solutions[C]certainly
   [D]stable[E]comprise[F]competitions
   [G]exactly[H]growth[I]included
   [J]role[K]progress[L]marvelous
   [M]challenges[N]combined[O]significant
【C11】

选项

答案N

解析 通过分析句子结构可知,when引导的时间状语从句省略了主语和be动词,结合句意可知,空格处填入的动词应该和alternative energy sources构成被动关系,因此空格处应填入动词的过去分词形式。结合该句句意可以推断,空格处所填的词有“结合”的意思,故N选项combined“使结合,联合”符合句意,为正确答案。
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