[SC求教]求解两道简单的比较题！

yi仪

OG 16-34题
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

选A，og对C的解释是：
C The construction so x as to y is not a correct idiom.

但是实际上，在 http://forum.chasedream.com/thread-141283-1-1.html 里面有说，so..as to不是一个正确的结构吗？

还有一道题：
In the 1980's the rate of increase of the minority population of the United States was nearly twice as fast as the 1970's.
划线部分：twice as fast as
A.不变
B.twice as fast as it was in
C.twice what it was in
D.two times faster than that of
E.two times greater than


答案是C，但是E是怎么错的？似乎他们都没讨论E，E有什么明显的错误吗？
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NicholeWhw

是不是只能是 so adj. as to........., 而用so debilitating it is这样的倒装不如A更优选

NicholeWhw

查到一个解释：So…as to用于单一主谓结构中，逻辑主语等于句子主语，即句子主语可以执行as to后动词所表达的动作