Q27:
If x and z are integers, is at least one of them even?
(1) x + z is odd.
(2) x - z is odd.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is
sufficient.
D. EACH statement ALONE is sufficient.

答案d. 我觉得应该是e.因为x+(-) z为奇数时，应该得不出至少x,z其中之一是偶数，如果两者都是偶数就不对。

理解题目问什么吧~问是否至少有一个是偶

那么有一个是偶或者两个是偶，对上面这个问题的答案都是“是”，答案唯一。选d

就是因为不能是奇~所以答案才确定...否定的答案也是唯一答案的一种...