How do you plan to solve it?
module demux1to4(d,s,y); input d; input [1:0] s; output [3:0]y; assign y[0] = ~s[1] & ~s[0] & d; assign y[1] = ~s[1] & s[0] & d; assign y[2] = s[1] & ~s[0] & d; assign y[3] = s[1] & s[0] & d; endmodule