Data Sufficiency

On Page 222 they have thus DS question
Is it true that X < Y?
1 5x < 5y
2 zx < zy

I thought the answer should be D. They say it is A.
Explaination is that in second statement Z could be +ve or -ve.

I chose D because we are already given zx < zy. Isn't it true that we have to assume that statement 2 is true.


Similarly on page 223

the question is
If X and Y are integers, does x = y?
1) xy = y2 (2 here is square)
2) x2 = y2 (2 here is square)

I thought the answer should be again D but the book says it is C.