请教nn一道语法题...谢谢:)

      A so gradual as to be indistinguishable

      B so gradual 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

C,D,E,都各自错在哪啊???谢谢

C: are unable to be distinguished  'cause it is wordy and "are unable to be" can't be used to instead of "can be"

D:"enough" ,the place of "not"

E:"enough so that"

Ets will say: BCD are awkward.............