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

• A

  ${\mathrm{C}}_2^{2-},{\mathrm{O}}_2^{-},\mathrm{CO},\mathrm{NO}$

• B

  ${\mathrm{NO}}^{+},{\mathrm{C}}_2^{2-},{\mathrm{CN}}^{-},{\mathrm{N}}_2$

• C

  ${\mathrm{CN}}^{-},{\mathrm{N}}_2,{\mathrm{O}}_2^{2-},{\mathrm{C}}_2^{2-}$

• D

  ${\mathrm{N}}_2,{\mathrm{O}}_2^{-},{\mathrm{NO}}^{+},\mathrm{CO}$