—I called you at about 8:30 last night but nobody answered.—Oh I in my office at that ti

问题补充：

—I called you at about 8:30 last night, but nobody answered.

—Oh, I in my office at that time.

A. worked B. was working C. will work

答案：

解析：at that time在那时，指对方打电话的时候，故应该用过去进行时，was/were+doing,故选B