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This is a tricky question. What if y=0 and x=1?
Consider A, xy=y^2 is true but, XY = X^2 isn't. So A is insuff.
Consider B, x and y can be negative and positive (1, -1). so xy can be + or - but X^2 is always positive.
If x=y=0, it is true
A => xy is +ve & B => |x| = |y|. So x,y = 3,3 or -4,-4 ... XY = X^2 is always true.