Prep 174,笔记的解释感觉怪怪的

summer3513

174.
Often major economic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the financial markets.
A.    so gradual as to be indistinguishable
B.    so gradual so that they can be indistinguishable
C.    so gradual that they are unable to be distinguished
D.    gradual enough not to be distinguishable  
E.    gradual enough so that one cannot distinguish them
选项分析：
A.    Correct. 主句为简单主系表结构
B.    so...so that搭配错误(Incorrect Idiom)
C.    able/unable to be done的结构错误
D.    enough偏向于主观判断，不符合逻辑语境；not to be distinguishable不如to be indistinguishable简洁
E.    enough so that错误搭配(Incorrect Idiom)
C为什么结构错误啊？哪里错了，我开始就选的C，望大牛帮忙解解，，，谢谢！

枫叶离殇

楼主有新PREP破解的笔记解释吗？能麻烦发到邮箱吗？？我的邮箱lx_zxf1989oo@foxmail.com
谢谢啦~~

summer3513

哇，，，斑竹，，谢谢！

毛毛carina

able/unable, 表示主语具备能力完成某个动作或某种行为，一般用于生命体，是不能用sth be able/unable to be done这种结构的