If \(x\) and \(y\) are different integers and \(x^2=xy\) which of the following must be true?

I. \(x=0\)
II. \(y=0\)
III. \(x=-y\)

(A) l only
(B) II only
(C) III only
(D) I and III only
(E) I, II, and III

Answer: A

Source: Official Guide