All the following are ambidentate ligands except

$$\begin{gathered} \mathrm{A}) {\mathrm{NO}}_2^{-}, {\mathrm{ONO}}^{-}; \mathrm{B}) {\mathrm{CN}}^{-}, {\mathrm{NC}}^{-} ; \mathrm{C}) {\mathrm{SCN}}^{-}, {\mathrm{NCS}}^{-} ; \\ \mathrm{These} \mathrm{are} \mathrm{ambidentate} \mathrm{ligands}; \\ \mathrm{But} \mathrm{oxalato} \mathrm{is} \mathrm{not} \mathrm{a} \mathrm{ambidentate} \mathrm{ligand}; \\ \mathrm{A} \mathrm{ligand} \mathrm{which} \mathrm{contains} \mathrm{two} \mathrm{donar} \mathrm{atoms} \mathrm{but} \mathrm{at} \mathrm{a} \mathrm{time} \mathrm{only} \mathrm{one} \mathrm{atom} \mathrm{donates} \mathrm{is} \mathrm{an} \mathrm{ambidentate} \mathrm{ligand}; \\ \mathrm{In} \mathrm{oxalato}, \mathrm{both} \mathrm{oxygen} \mathrm{atoms} \mathrm{can} \mathrm{donate} \mathrm{simultaneously}; \end{gathered}$$