so x as to y 的结构到底可不可用

飞飞5816

37.    Although schistosomiasis is not often fatal, it is so debilitating that it has become an economic drain on many developing countries.
(A)    it is so debilitating that it has become an economic
(B)    it is of such debilitation, it has become an economical
(C)    so debilitating is it as to become an economic
(D)    such is its debilitation, it becomes an economical
(E)    there is so much debilitation that it has become an economical

Og里面C选项说 The construction so x as to y is not a correct idiom，但是prep08里又有这样的句子Often major economic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the financial markets.
请教各位NN这个结构到底可不可用呢

michaelmay17

它是有对的时候，简单来说如果主语不一致so as to 就会错