In the last ten years, they _______ three great scientific experiments. 
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A
finished
B
have finished
C
had finished
D
have been finished
推荐题目
When you get the paper back,pay special attention to what______.
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A
have marked
B
have been marked
C
had marked
D
had been marked
These days, we _____ for our final exams.
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A
are prepared
B
have prepared
C
are preparing
D
will prepare