From the stability constant (hypothetical values) given below,predict which is the strongest ligand:

• A
  $Cu^{2+} + 4NH_3 \rightleftharpoons [Cu(NH_3)_4]^{2+}, K = 4.5 \times 10^{11}$
• B
  $Cu^{2+} + 4CN^{-} \rightleftharpoons [Cu(CN)_4]^{2-}, K = 2.0 \times 10^{27}$
• C
  $Cu^{2+} + 2en \rightleftharpoons [Cu(en)_2]^{2+}, K = 3.0 \times 10^{15}$
• D
  $Cu^{2+} + 4H_2O \rightleftharpoons [Cu(H_2O)_4]^{2+}, K = 9.5 \times 10^8$