It is not a good habit _________ in public places.

题目

It is not a good habit _________ in public places.
to do sth 还是 doing sth?

答案

doing
examples:
It is not a good habit smoking in public places.
(since it is a habit,you are doing that already.To do something means haven;'t done yet.)
you can say,
It is not good to smoke in public places.