08 prep 174 讨论贴上找不到答案~求助~

pye34878

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(A)

E.gradual enough so that one cannot distinguish them

哪位高手能帮忙解释下C为什么不对呢？

ffen

be unable to be done是awkward的用法