You got back so late and you didn’t even give me a proper reason you hadn’t called me! I’m very unhappy with you.
A. when
B. why
C. how
D. which
网友回答
A. when
(答案→)B. why
C. how
D. which
解析：考查定语从句：先行词是a proper reason定语从句中不缺主宾表，缺少原因状语，句意：你回来这么迟，你没有给我合理的解释为什么没有打电话给我！我对你很不满意。选B。