Unlike a hurricane, which can be observed from within, 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 impractical

(C) for such studies as this to have been impractical

(D) as to not make such a study practical（A）

(E) as to be impractical of study

答案选a,我选的e,我觉得a 的such a study,study之前没有出现过,怎么可以用such呢,请大侠赐教呀!

可以这样用么/,study概括be observed,但是such是特指