Cardiovascular system has to do with the heart, so anything to reduce the risk of that system (including the heart, bloodstream etc.) would be the answer for you. So just using Process of elimination:
A) Has to do with external exposure. <em>No</em><em />
B) Keeping hands clean <em>No</em><em />
C) Avoiding cigarette smoke <em>Yes</em>
D) Keeping your vaccinations up to date <em>No</em><em />
So your answer is C.
I think that aerobic is where you do physical activities to release oxygen
Stay, driving drunk is a risk of hurting yourself and/or others
