Leaching of gold with dilute aqueous solution of $NaCN$ in presence of oxygen gives complex $[A]$,which on reaction with zinc forms the elemental gold and another complex $[B]$. $[A]$ and $[B],$ respectively are ...... .

• A
  $[Au(CN)_4]^-$ and $[Zn(CN)_2(OH)_2]^{2-}$
• B
  $[Au(CN)_2]^-$ and $[Zn(OH)_4]^{2-}$
• C
  $[Au(CN)_2]^-$ and $[Zn(CN)_4]^{2-}$
• D
  $[Au(CN)_4]^{2-}$ and $[Zn(CN)_6]^{4-}$