双肾积水最常见的原因为（）
A.双输尿管狭窄
B.输尿管结石
C.下尿路梗阻
D.膀胱肿瘤
E.输尿管畸形
参考答案：C
I didn't know this ______ he told me. [ ]
A. after
B. before
C. until
D. B and C
简述胃癌的鉴别诊断。
