Which is a pair of ambidentate lignands among the following?

• A

  ${\mathrm{CN}}^{-},{\mathrm{NO}}_2^{-}$

• B

  ${\mathrm{NO}}_3^{-},{\mathrm{NO}}_2^{-}$

• C

  ${\mathrm{CNS}}^{-},{\mathrm{C}}_2{\mathrm{O}}_4^{-2}$

• D

  ${\mathrm{C}}_2{\mathrm{O}}_4^{-2},{\mathrm{SO}}_4^{-2}$