`timescale 1ns/1ns module add_4( input [3:0] A , input [3:0] B , input Ci , output wire [3:0] S , output wire Co ); wire [3:0]S1; wire [3:0]S2; add_full u1( .A(A[0]), .B(B[0]), .Ci(Ci), .S(S1[0]), .Co(S2[0]) ); add_full u2( .A(A[1]), .B(B[1]), .Ci(S2[0]), .S(S1[1]), .Co(S2[1]) ); add_full u3( .A(A[2...