-----Were you at home at 9 o’clock last night?---Yes I a shower at that time.A. tookB.

问题补充：

-----Were you at home at 9 o’clock last night?

-----Yes, I a shower at that time.

A. took

B. was taking

C. was taken

D. am taking

答案：

A. took

(答案→)B. was taking

C. was taken

D. am taking

解析：句意：昨晚九点钟你在家吗？——是的，那时我正在洗澡。结合语境可知下文描述的是过去某时正在进行的动作，故用过去进行时态。选B。