请教大全section21-15

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）

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

答案D 为什么不好,因为多了they?但我认为,but前后两个独立的句子比E更对称.

请NN指点一下.多谢!!

问题在于D中的every time不能作为连词来引导从句 fuel became scarce and expensive，你可以把它看作一个副词词组。

所以在E中被替换成了whenever。

but they forget，but forget这两种说法这里都是可以的。

后面分句的连词是BUT，所以可以使用every time副词做状语。

但好像but后有两个谓语哟？

抱歉，抱歉，那时偶两眼SO昏花，AS TO没看清楚题目。

我们把句子补全吧：

(D) discover the principles of solar energy every time fuel became scarce and expensive, but they forget them every time a new source of cheap energy is developed.

(E) discover the principles of solar energy whenever fuel becomes scarce and expensive but forget them every time a new source of cheap energy is developed.

D中并列句的时态不对等。

查了语法书，every time 可以作为关系副词引导从句 。

以下是引用jerjer在2005-3-17 16:13:00的发言：

抱歉，抱歉，那时偶两眼SO昏花，AS TO没看清楚题目。

我们把句子补全吧：

(D) discover the principles of solar energy every time fuel became scarce and expensive, but they forget them every time a new source of cheap energy is developed.

(E) discover the principles of solar energy whenever fuel becomes scarce and expensive but forget them every time a new source of cheap energy is developed.

D中并列句的时态不对等。

查了语法书，every time 可以作为关系副词引导从句 。

我也是大脑停电，神经搭错桥~~~我要骂粗口了#$%!^

这么明显的错没看出来！！

谢谢了！！