OT: Another SAT Question of the Day

Note: Those 2s should be up in the corner. Didn't copy and paste
that way.
I already chose the wrong answer....apparently I'm not alone - only
29% have gotten it right so far.

If (x + y)2 = x2 + y2, which of the following statements must also be
true?

x = 0
(x – y)2 = x2 + y2
xy = 0


A. None
B. I only
C. II only
D. III only
E. II and III
.