关于so as to的用法，特来求教

OG 33

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

答案为A

我选择了C，虽然是个倒装，但是我没不知道so as to在这个句子里面有什么错误，我搜索了一下有人说so as to后应当接be 而不接其他动词。不知道这个说法是否正确

大家帮忙解释一下C错在哪里，另外so as to可以用成这样的倒装吗？谢谢了