module mux2 (S,A,B,Y);
    input S;
    input A,B;
    output reg Y;

    always @(*)
		Y = (S)? B : A;
endmodule

module mux4 ( S, D, Y );
    input[1:0] S;
    input[3:0] D;
    output Y;

    reg Y;
    wire[1:0] S;
    wire[3:0] D;

    always @*
    begin
        case( S )
            0 : Y = D[0];
            1 : Y = D[1];
            2 : Y = D[2];
            3 : Y = D[3];
        endcase
    end
endmodule

module mux8 ( S, D, Y );
    input[2:0] S;
    input[7:0] D;
    output Y;

    reg Y;
    wire[2:0] S;
    wire[7:0] D;

    always @*
    begin
        case( S )
            0 : Y = D[0];
            1 : Y = D[1];
            2 : Y = D[2];
            3 : Y = D[3];
            4 : Y = D[4];
            5 : Y = D[5];
            6 : Y = D[6];
            7 : Y = D[7];
        endcase
    end
endmodule

module mux16 (D, S, Y);
 	input  [15:0] D;
 	input  [3:0] S;
 	output Y;

    assign Y = D[S];
endmodule