**Core Concept**
The question tests the understanding of **selective serotonin reuptake inhibitors (SSRIs)**, specifically focusing on their pharmacokinetic properties. SSRIs are a class of drugs commonly used to treat **depression** and other **mood disorders**. A prodrug is a medication that is metabolized into its active form within the body.

**Why the Correct Answer is Right**
The correct answer is based on the knowledge that one of the SSRIs is administered as an inactive compound, which is then converted into its active form through metabolic processes in the liver. This prodrug is **citalopram's** predecessor in some aspects but specifically, it's about **fluoxetine** being a prodrug that is metabolized into its active metabolite, **norfluoxetine**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not specifically known as a prodrug.
**Option B:** Incorrect as it does not require transformation to be active.
**Option D:** Incorrect because, similar to option A, it is not a prodrug.

**Clinical Pearl / High-Yield Fact**
Remembering that **fluoxetine** has a long half-life due to its active metabolite **norfluoxetine** is crucial for clinical practice, as it influences dosing and potential side effects.

**Correct Answer:** D. Fluoxetine