
Create a 16-bit wide, 9-to-1 multiplexer. sel=0 chooses a, sel=1 chooses
b, etc. For the unused cases (sel=9 to 15), set all output bits to '1'.

module TopModule (
  input [15:0] a,
  input [15:0] b,
  input [15:0] c,
  input [15:0] d,
  input [15:0] e,
  input [15:0] f,
  input [15:0] g,
  input [15:0] h,
  input [15:0] i,
  input [3:0] sel,
  output logic [15:0] out
);

