I’m not sure whether be has finished writing the book but he it last month.A. worked at B

问题补充：

I’m not sure whether be has finished writing the book, but he it last month.

A. worked at

B. was working on

C. worked on

D. was working at

答案：

A. worked at

(答案→)B. was working on

C. worked on

D. was working at

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