In this question, X = x2x1x0 and Y = y1y0. So, X ranges from 000 to 111 and Y ranges from 00 to 11. For f to be 1, X must be >Y. In my opinion, it is easier to verify the options than to try to form an expression and then simplify it. For verification, take a value of Y (say 11). Now values of X from 100 to 111 should lead to f=1 and X from 000 to 011 should lead to f=0.