please look carefully before you_____(cross)the street.请运用适当的形式填空并说明道理.
问题描述：
please look carefully before you_____(cross)the street.请运用适当的形式填空并说明道理.
答
cross
这里before是介词后面加从句,you_____(cross)the street.这一句子缺少了谓语,又考虑时态一般现在时比较恰当.故用cross.