题目内容
Look out for cars _____ the street.
A. when crossed B. when crossing
C. if you crossed D. while you were crossing
B
用现在分词短语表示伴随。

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题目内容
Look out for cars _____ the street.
A. when crossed B. when crossing
C. if you crossed D. while you were crossing
B
用现在分词短语表示伴随。