**Core Concept**
The question tests the understanding of pharmacokinetics, specifically the concept of prodrugs. A **prodrug** is a medication or compound that, after administration, is metabolized into a pharmacologically active drug.

**Why the Correct Answer is Right**
The correct answer is a drug that requires metabolic conversion to become active. This process typically occurs in the liver, where enzymes such as **cytochrome P450** convert the inactive prodrug into its active form. The active form then exerts the therapeutic effect.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not represent a commonly recognized prodrug.
**Option B:** Similarly, this option does not fit the description of a prodrug that is inactive when given orally.
**Option C:** This choice is also incorrect as it is not typically classified as a prodrug.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that prodrugs are often used to improve bioavailability, reduce side effects, or enhance the drug's efficacy.

**Correct Answer:** D. Levodopa