We must know what we should do and what we should avoida _________ good impression on others in public place．
A.to leaveB.leavingC.to have leftD.leave在线课程A
解析：
句意：我们必须知道在公共场合应当做什么，应当避免什么以给别人留下一个好印象。空格处是目的状语，所以要用不定式。