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 an 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 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 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
【S1】
【S2】
【S3】
【S4】
【S5】
【S6】
【S7】
【S8】
【S9】
【S10】
题目内容
（请给出正确答案）
简答题官方参考答案
（由简答题聘请的专业题库老师提供的解答）
