JEE Main Chemistry question

From the (hypothetical) stability constants given below, predict which is the strongest ligand.

• (A)Cu^{2+}+4NH_3\rightleftharpoons[Cu(NH_3)_4]^{2+};
• (B)Cu^{2+}+4CN^-\rightleftharpoons[Cu(CN)_4]^{2-}; Correct
• (C)Cu^{2+}+2en\rightleftharpoons[Cu(en)_2]^{2+};
• (D);