Rocky Mountain Spotted Fever
If you don't know how that kind of thing works, you are likely to make mistakes regarding it. If you know how it works, you can prevent yourself from making mistakes that could endanger yourself and/or others.
Answer: C: Using your refusal skills!
Explanation: HIV is transmitted through bodily fluids and sexual contact. Using illegal drugs is not only harmful (most likely), but you are not maintaining safety measures. There is no vaccine for HIV as of now, so injecting drugs would not me a preventative measure. Engaging in sexual activity with multiple partners is one of the ways TO CONTRACT HIV, even when using protection. If you don't use universal precautions in a healthcare setting, you can contract HIV (although not as likely). So the best way to reduce your chances of HIV would be to use universal precautions, use protection, or the best way, use refusal skills.