大学英语四级选词填空练习（三十一）

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