Which of the following complexes formed by `Cu^(2+)` ions is most stable ?

Options

A. `Cu^(2+)+4NH_3 harr [Cu(NH_3)_4]^(2+)`, log K =11.6
B. `Cu^(2+)+4CN^(-) harr [Cu(CN)_4]^(2-)`, log K =27.3
C. `Cu^(2+)+ 2en harr [Cu(en)_2]^(2+)`, log K =15.4
D. `Cu^(2+)+ 4H_2O harr [Cu(H_2O)_4]^(2+)`, log K = 8.9