四级阅读选词填空题的两原则和五“定”法
l play a growing 51 in the world’s energy supply. But experts say that even when 52, alternative energy sources will likely meet only about 30% of the world’s energy needs by 2050.
For example, even with 53 investments, such as the $93 million for wind energy development 54 in the American Recovery and Reinvestment Act, important alternative energy sources such as wind and bio-fuels 55 o
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