Based on the given stability constants (hypothetical values),predict which is the strongest ligand?

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