Which health factor is outside your individual control?
using proper safety equipment such as helmets
having a safe or clean living environment
having a support structure of people you can count on for advice

Either B or C depending on your situation. As a young person still living in their parents house, maybe you can't ensure your environment is safe or clean. Having a support structure is largely reliant on just who is around you, which you can't necessarily control (can't just pack up and move every time you can't find someone to depend on).