Which behavior will help someone avoid STls?

A. Changing partners frequently
B. Avoiding the need for treatment
C. Understanding the risks of sexual activity
D. Thinking it can't happen to me

C. Understanding the risks of sexual activity

The behavior that will help someone avoid sexually transmitted infections (STIs) is C. Understanding the risks of sexual activity.

It is important to have knowledge about the risks associated with sexual activity and how STIs are transmitted. This includes understanding the importance of using protection, such as condoms, getting regular STI testing, and practicing safe and responsible sexual behavior.

Changing partners frequently (option A) does not necessarily help avoid STIs, as each new sexual partner introduces the possibility of exposure to infection. Avoiding the need for treatment (option B) is not a recommended approach, as untreated STIs can lead to serious health complications. Thinking it can't happen to me (option D) is a dangerous mindset that can lead to risky behavior and potential exposure to STIs.