Answer B. If it said X^2 + Y^2 divisible by 8 then the answer would be C, because they would both have to be even, and their sum, divisible by 8. But it says X^2 - Y^2, so all we need is their sum divisible by 8 to tell us their sum is an integer.
X and Y are even integers, not enough. (statement 2 also lets us know they are integers)
X+Y is divisible by 8.
take 16, X=3, Y=13. X^2 - Y^2=160. divisible by 8
24 X=3, Y=21. X^2 - Y^2=432. divisible by 8
Try it with X^2 + Y^2 there you will need both numbers to be even.
Let us to't pell-mell...