I think option 'D' is the correct answer.
Since we have to do either of the following operations
x=y*y or y=x*x
before
x=x-y or y=y-x
the sum of resultant numbers need to be a perfect square
A.x=2 y=2 ;x+y=4(perfect square)
B.x=5 y=-1 ;x+y=4(perfect square)
C.x=-63 y=72;x+y=9(perfect square)
D.x=32 y=5;x+y=37(not a perfect square)