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