急救:一道语法题目!!!!:)谢谢(大全214)

Climatic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the weather.

A so gradual as to be indistinguishable

B  so gradual they can be indistinguishable

C  so gradual that they are unable to be distinguished

D  gradual enough not to be distinguishable

E  gradual engough so that one cannot distinguish

c  错在哪里啊?

答案是A吗？

Choice A, the best answer, presents the idiomatic form (some things) are so X as to be Y. Choice B,C,D, and E can be faulted for not following this form. In addition, C confusedly refers to the climatic shifts themselves as being unable when it is really people who are unable at first to distinguish climatic shifts. This is a very difficult question.

另外be able/unable to do不能用被动语态

答案是a,只是解释还是没太懂......能详细点解释下不???

阅读大全里面有个选项：

(C) Its recurrence is unlikely to be able to be predicted by scientists.

另，unable to be没有出现