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 (基础设施) and jobs. Underling all this __1__ 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 __2__. sustainable way is the cornerstone (基石) of our nation's energy security, and will be one of the major __3__ of the 21st century. Alternative forms of energy- bio-fuels, wind and solar, to name a few are __4__ being funded and developed, and will play a growing __5__ in the world's energy supply. But experts say that even when __6__, alternative energy sources will likely meet only about 30% of the world's energy needs by 2050.

　　For example, even with __7__ investments, such as the $93 million for wind energy development __8__ in the American Recovery and Reinvestment Act, important alternative energy sources such as wind and bio-fuels __9__ 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 __10__ both traditional and alternative.

　　[A] stable

　　[B] solutions

　　[C] significant

　　[D] role

　　[E] progress

　　[F] marvelous

　　[G] included

　　[H]growth

　　[I] exactly

　　[J] consist

　　[K] comprise

　　[L] competitions

　　[M] combined

　　[N] challenges

　　[O] certainly

　　答案解析：

　　1 growth 2 stable 3 challenges 4 certainly 5 role 6 combined 7 significant 8 included 9 comprise 10 solutions

　　【解析】这是一篇讨论能源资源的说明文，话题是考生比较熟悉的能源问题，不断增长的人口与可再生资源的矛盾该如何解决。文中指出能源的一些可替代形式 如生物能源、风能太阳能等可再生资源将在未来发挥越来越重要的作用。但是专家指出，即使这些资源储备量惊人，但是到2050年也只能满足世界30%的需求。文章最后两段探讨了各能源在市场上的需求，以及解决未来能源需求的其他方案。

　　总体来说，这篇文章理解难度不大，填空难度适中，所选词汇也都是四级考纲的词汇。选项较具有干扰项，多为c和s开头的单词，考生在考试时要特别注意。