— I rang you at about nine, but there was no reply.
— Oh, that was probably I was seeing the doctor.
A. why
B. when
C. what
D. That
网友回答
A. why
(答案→)B. when
C. what
D. That
解析：句意：--昨晚我打电话给你,但是没有人接电话。--哦，那很有可能我正在看医生。依据上下文was后应是表时间的表语从句，只能用when来引导。
考点: 考查表语从句关系词的用法。