What is the decreasing order of strength of the bases $OH^-, NH_2^- , H-C\equiv C^-$ and $CH_3CH_2^-$ ?

Question

(a) $CH_3CH_2^- > NH^-_2 > H-C \equiv C^- > OH^-$

(b) $H-C\equiv C^- > CH_3-CH^-_2 > NH_2^- > OH^-$

(c) $OH^- > NH^-_2 > H-C\equiv C^- > CH_3-CH^-_2$

(d) $NH^-_2 > H-C\equiv C^- > OH^- > CH_3CH_2^-$.