请教数学JJ154题目....

154.  n is positive integer, 9*n=xyz, xyz is a three-digit number, x=1~9; y,z=0~9, x+y+z=9?

(1) x+y+z<15

(2) x+y+z>8

Ans: A

(1) x+y+z只可以为9

(2) x+y+z可以为9, 18, 27 →
            非唯一解

请问下牛牛们思路如何.....

谢谢~