高手，求助一道题，谢谢了

lijia1301981

Q13:

If x + y is an integer, is y an integer?

(1)    x – y is an integer.

(2)    x + 2y is an integer.

              

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.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer: B

为什么第一个条件不对呢

intersun

X=1.5 y=0.5

winsn

X+Y=某个整数,

条件1,X-Y=某个整数,

那么X+Y-(X-Y)=2Y=某个整数

所以Y=某个整数/2

不能确定Y是否整数