下列句子中，加点成语使用最恰当的一项是 （ ）

Smoking is not allowed in public places since May 1st. It may be a good chance for some people to ______ smoking.

－What were you doing when you heard Eastern Star went down in the river－I my homework.

I went to Sanya with my family this summer andall of us _____ a good trip.

The doctor often tells him _____________more exercise.