`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 [4:1] C_reg; add_full add_full_inst1 ( .A (A[0]), .B (B[0]), .Ci(Ci), .S (S[0]), .Co(C_reg[1]) ...