问题描述：
the math teacher gave us some exercises and asked us ______选哪个,为什么?
the math teacher gave us some exercises and asked us ______
A. to work them on B. working them on C. to work on them D. working on them
the math teacher gave us some exercises and asked us ______
A. to work them on B. working them on C. to work on them D. working on them
问题解答：
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