He was so busy that he couldn’t help ____________ the experiment.A．doingB．doC．di_刷题宝

题干

He was so busy that he couldn’t help ____________ the experiment.

A．doing

B．do

C．did

D．done

上一题下一题 0.64难度单项选择更新时间:2013-01-05 09:16:10

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