请教一道语法

dedeyuky · 发表于 2011-9-10 23:23:37

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

答案选E。求解释~~

dedeyuky · 发表于 2011-9-11 22:07:37

dedeyuky · 发表于 2011-9-11 22:08:59

497460618 · 发表于 2011-9-12 11:50:58

首先,没有现在完成时的标志词SINCE,THE LAST N YEARS等，所以排除A,B,C.E更符合原文本意，并且遵循有仇报仇原则。。。。。。

请教一道语法

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