问题
选择题
I'm not sure whether he 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
答案：B
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I'm not sure whether he 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：B