问题描述：
The students here ______ all kinds of exercises every day in the past four days.
A.have been kept busy doing B.have kept busy doing
C.kept busy doing D.keep on doing
不明白怎么会是被动
A.have been kept busy doing B.have kept busy doing
C.kept busy doing D.keep on doing
不明白怎么会是被动
问题解答：
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