The risk factor that you can control from the options provided is related to your friends starting to smoke. While you cannot control your friends' decisions, you can control your own decision to be influenced by their behavior and choose not to smoke or engage in the activity.
The other factors mentioned (family history of heart disease, ethnic incidence of high blood pressure, and unintentional accidents) are not controllable by you.
So the best answer would be: You can control your own response to your friends smoking.