**Core Concept**
Vitamin C is an essential cofactor for several enzymes in the human body, particularly those involved in collagen synthesis and iron absorption. These enzymes rely on vitamin C to maintain their activity and function properly.

**Why the Correct Answer is Right**
One such enzyme is prolyl hydroxylase, which is crucial for the stabilization and cross-linking of collagen molecules. Prolyl hydroxylase requires vitamin C as a cofactor to facilitate the hydroxylation of proline residues in collagen. This process is essential for the formation of a stable collagen triple helix structure. Additionally, vitamin C-dependent enzymes like lysyl oxidase are also involved in collagen cross-linking and stabilization.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify an enzyme that requires vitamin C for its activity.
**Option B:** This option is incorrect because it does not mention a vitamin C-dependent enzyme.

**Clinical Pearl / High-Yield Fact**
Vitamin C deficiency can lead to scurvy, a condition characterized by impaired collagen synthesis and iron absorption. This can result in symptoms such as fatigue, joint pain, and poor wound healing.

**Correct Answer: D.**