If x > y and y > z, which of the following represents the greatest number?

[BTGmoderatorLU]

Source: Official Guide

If x > y and y > z, which of the following represents the greatest number?

A. x - z
B. x - y
C. y - x
D. z - y
E. z - x

The OA is A

[Brent@GMATPrepNow]

Source: Official Guide

If x > y and y > z, which of the following represents the greatest number?

A. x - z
B. x - y
C. y - x
D. z - y
E. z - x

The OA is A

The key here is to recognize that there is only ONE correct answer.
So, as long as we find values that satisfy the given conditions (x > y and y > z), we can simply test the answer choices.

If x > y and y > z, then it could be the case that x = 1, y = 0, and z = -1
We'll now plug these values into the five answer choices....
(A) x − z = 1 - (-1) = 2
(B) x − y = 1 - 0 = 1
(C) y − x = 0 - 1 = -1
(D) z − y = (-1) - 0 = -1
(E) z − x = (-1) - 1 = -2

Answer: A