Consider the following sentences as a paragraph. Choose the topic sentence you think expresses the main idea.

A、Ifyoustopcarryingmatchesoralighter,youcancutdownonimpulsesmoking.;
B、Ifyousitinno-smokingareas,youwillsmokeless.;
C、Youcanbehaveinwaysthatwillhelpyousmokeless.;
D、Bykeepingarecordofwhenandwhereyousmoke,youcanidentifythemosttemptingsituationsandthenavoidthem.