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People have discovered the principles of solar energy whenever fuel becomes scarce and expensive but will forget them every time a new source if cheap energy is developed.

A.     have discovered the principles of solar energy whenever fuel becomes scarce and expensive but will forget

B.     have discovered the principle of solar energy whenever fuel has become scarce and expensive but they forget

C.     discovered the principles of solar energy every time fuel becomes scarce and expensive, forgetting

D.    discover the principles of solar energy every time fuel became scarce and expensive, but they forget

E.     discover the principles of solar energy whenever fuel becomes scarce and expensive but forget

whenever fuel becomes scarce and expensive, people discover, 这个好像是从句， 可是拆不开， 有点不理解啊！

这个题目其实很基本阿

文章的原意大概是：人们每次在燃料稀缺和昂贵的时候去开发关于太阳能的一些理论，但是却在每次新的便宜能源被开发出来时忘记这些理论。

首先这里文章描述的是一个经常性习惯性的动作，应该使用一般现在时 所以使用完成时态 和过去时态 都是没有道理的 排除A B C D

直接得到E这个答案....

至于whenever fuel becomes scarce and expensive, people discover...这句话么

前面whenever引导时间状语从句到expensive为止，后面就是主句了，当然主句后面还跟着一个if条件状语从句。

whenever=no matter when

表达一种强烈语气

[em17]