**Core Concept**
Selective serotonin reuptake inhibitors (SSRIs) are a class of medications used to treat depression, anxiety disorders, and other conditions by increasing serotonin levels in the brain. The duration of action of an SSRI can vary significantly between different drugs, affecting their dosing frequency and patient adherence.

**Why the Correct Answer is Right**
Fluoxetine (Prozac) is known for its long half-life, which allows it to be administered once daily. Its active metabolite, norfluoxetine, has an even longer half-life, contributing to its prolonged duration of action. This pharmacokinetic profile enables fluoxetine to maintain therapeutic levels in the body for an extended period, making it the longest-acting SSRI.

**Why Each Wrong Option is Incorrect**
**Option A:** Fluvoxamine has a shorter half-life compared to fluoxetine and requires twice-daily dosing.
**Option B:** Paroxetine has a moderate half-life but is known for its potential for drug interactions and is not the longest-acting SSRI.
**Option C:** Sertraline has a moderate half-life and is commonly dosed once daily but is not as long-acting as fluoxetine.

**Clinical Pearl / High-Yield Fact**
When choosing an SSRI, consider the patient's dosing adherence and potential for medication interactions. Fluoxetine's long half-life can be beneficial in patients with poor adherence or those requiring concomitant medication.

**Correct Answer: C. Sertraline. Sertraline.**