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

A、 If you stop carrying matches or a lighter, you can cut down on impulse smoking.;
B、 If you sit in no-smoking areas, you will smoke less.;
C、You can behave in ways that will help you smoke less.;
D、By keeping a record of when and where you smoke, you can identify the most tempting situations and then avoid them.