Which one of the following constitutes a group of the isoelectronic species?

Question

( A ) $CN^-, N_2 , O_2^{2-}, C_2^{2-}$
( B ) $N_2 , O_2^{-}, NO^{+}, CO$
( C ) $NO^+, C_{2}^{2-}, CN^-, N_2$
( D ) $C_2^{2-}, O^{-}_2, CO, NO$