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

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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 have on everything from food and water to infrastructure (基础设施) and jobs. Underlying all this【S1】______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【S2】______. sustainable way is the cornerstone (基石) of our nation’s energy security, and will be one of the major【S3】______of the 21st century. Alternative forms of energy — bio-fuels, wind and solar, to name a few — are【S4】______being funded and developed, and will play a growing【S5】______in the world’s energy supply. But experts say that, even when【S6】______, alternative energy sources will likely meet only about 30% of the world’s energy needs by 2050.
    For example, even with【S7】______investments, such as the $93 million for wind energy development【S8】______in the American Recovery and Reinvestment Act, important alternative energy sources such as wind and bio-fuels【S9】______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 【S10】______— both traditional and alternative.
[A] stable               [F] marvelous                   [K] comprise
[B] solutions            [G] included                    [L] competitions
[C] significant          [H] growth                      [M] combined
[D] role                 [I] exactly                     [N] challenges
[E] progress             [J] consist                     [O] certainly
【S3】

选项

答案N

解析 空前的one of和形容词major以及空后的of表明,本空应填一复数名词,[B]、[L]和[N]入选。结合语境,寻找资源以应对需求应该是一种挑战,故答案为[N]challenges"挑战”。[B]solutions"解决办法”和[L]competitions“比赛”均不符合此处语义。
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