We must know what we should do and what we should avoid a good impression on others in pu

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。