**Core Concept**
Anti-HIV agents are a class of medications used to treat or prevent HIV infection. They work by targeting various stages of the HIV life cycle, including viral entry, replication, and integration into the host cells.

**Why the Correct Answer is Right**
The correct answer is **Ritonavir**. Ritonavir is a protease inhibitor (PI) used in combination with other anti-HIV agents to treat HIV infection. It works by inhibiting the protease enzyme, which is essential for the maturation of viral particles. By blocking this enzyme, ritonavir prevents the production of new viral particles.

**Why Each Wrong Option is Incorrect**
**Option A:** None provided
**Option B:** None provided
**Option C:** None provided

**Clinical Pearl / High-Yield Fact**
Ritonavir is often used as a pharmacokinetic booster to enhance the levels of other protease inhibitors, such as atazanavir and darunavir, by inhibiting the CYP3A4 enzyme.

**Correct Answer: C. Ritonavir**