Which of the following group show +M and -I effect?
(A) $\ce{-\underset{\underset{\huge O}{||}}{C}-F}$
(B) $\ce{-\underset{\underset{\huge O}{||}}{C}-OR}$
(C) $\ce{-O^-}$
(D) $\ce{-OH}$
Answer is option D. D is obviously correct, but why not option C? $\ce{-O^-}$ has electrons to donate and is electronegative.