问题补充:
We must know what we should do and what we should avoid a good impression on others in public places.
A. to leave
B. leaving
C. to have left
D. leave
答案:
(答案→)A. to leave
B. leaving
C. to have left
D. leave
解析:句意:在公共场合,为了给其他人留一个好的印象,我们必须知道我们该做什么,我们应该避免做什么。表示目的“为了……”,故用不定式,选A。