Which of the given compound is flexidentate as well as ambidentate ligand ?

• A

  ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$

• B

  ${\mathrm{CN}}^{-}$

• C

  ${\mathrm{OCN}}^{-}$

• D

  ${\text{ EDTA }}^{4-}$