Among the options provided, the risk factor you can control is related to your behavior and choices. While family history, ethnic predispositions, and certain statistics about accidents are outside of your control, you can control your own health choices and behaviors.
However, none of the provided options directly involve something you can change. But if we think about social influences, such as your friends smoking, while you cannot control their choices, you can choose how to respond to that influence (e.g., avoiding smoking yourself).
Therefore, the most relevant choice would be:
Your friends have recently started smoking. (You have the choice to not smoke, which is a behavior you can control.)