What is the decreasing order of strength of the bases $OH^-,NH_2^-,H-C \equiv C^-$ and $CH_3 ^{-}CH_2^-$?

$(a)\;CH_3 - CH_2 > NH_2 > H-C \equiv C^- > OH^- \\ (b)\;H-C \equiv_3 - C^- > CH_3 - CH_2^- > NH_2 > OH^- \\ (c)\;OH^- > NH_2^{-} > H-C \equiv C^- > CH_3 -CH_2^- \\ (d)\;NH_2 > H-C \equiv C^- > OH^ > CH_3 - CH_2^-$

The conjugate base of a strong acid is weaker while the conjugate base of weak acid is stronger.
So $CH_3 - CH_2 > NH_2 > H-C \equiv C^- > OH^-$
Hence a is the correct answer.