—I rang you at about nine but there was no reply.—Oh that was probablyI was seeing the d

问题补充：

—I rang you at about nine, but there was no reply.

—Oh, that was probablyI was seeing the doctor.

A. why

B. when

C. what

D. that

答案：

A. why

(答案→)B. when

C. what

D. that

解析：when引导表语从句，表示时间。故选B。