请教一道语法题

zhengqingku

Unlike a hurricane, which can be observed from withn, a tornado is so small that such a study has not been practical.
A. that such a study has not been practical
B. that studying it that way has not been impratical
C. for such studies as this ti have been impractical
D. as to not make such a study practical
E. as to be impractical of study

答案选A。看了很多帖子，还是不懂E错在哪。。请大家指教！！

lovesiqi4665

so ... as to ... 前后主语一致，tornado 怎么会impractical 呢？ 是说study impractical

hjbb1027

so … as to事实上是三个结构的结合，so引出的是状语，as指代句子前面的核心含义，to是不定式引导状语结构(adverbial structure)，此不定式修饰的正是前面的核心动词以及该动词的逻辑主语，所以只有当前面只有一个核心动词而且很明确的时候才能够用so…as to，也正因为修饰成分离被修饰词过远会造成修饰不清，所以to be/do结构不能与前面动词不能太远。


所以对于E选项，be impractical的主语变成tornado，在逻辑上应该是不通的。

而例如，I'm not so stupid as to believe that.这句话，believe的动作是I发出的，才可以用so...as to...结构表达。

个人之见，嘿嘿

zhengqingku

谢谢LS两位！！灰常明白！！