module mux2x1(A,B,select,OUT); 
   input A,B,select; 
   output OUT; 
   reg OUT; 
   always @ (select or A or B) 
         if (select == 1) OUT = A; 
         else OUT = B; 
endmodule 

module testmux; 
  reg TA,TB,TS;            //inputs for mux 
  wire Y;                  //output from mux 
  mux2x1 mx (TA,TB,TS,Y);  // instantiate mux 
     initial 
        begin 
              TS = 1; TA = 0; TB = 1; 
          #10 TA = 1; TB = 0; 
          #10 TS = 0; 
          #10 TA = 0; TB = 1; 
        end 

     initial 
      $monitor("select = %b A = %b B = %b OUT = %b time = %0d", 
               TS, TA, TB, Y, $time); 
endmodule