If x + y - z = 5 and x - y + z = 10, which of the following statements MUST be true?
I. y > z
II. X > 5
III. Y > 5
A. I and II only.
B. II and III only.
C. III only.
D. I only.
E. II only.
Adding the equations gives 2x = 15 or x = 7.5. So, x > 5 (II is true). Substituting x = 7.5 gives z - y = 2.5. So, z > y (I is false). There are no further conditions on y. So, III is not necessarily true.