– I rang you at about ten o’clock but there was no reply.– Oh that was probably I was s

问题补充：

– I rang you at about ten o’clock, but there was no reply.

– Oh, that was probably I was seeing the doctor.

A. when

B. why

C. what

D. that

答案：

(答案→)A. when

B. why

C. what

D. that

解析：考查表语从句：表语从句部分I was seeing the doctor.不缺主宾表， 说明不能用what，根据句意：--10点我打电话给你，但没人接。--那可能是我去看医生的时候。选A。