## Core Concept
The question tests the understanding of wound healing, specifically the role of nutritional factors in collagen assembly during scar tissue formation. Collagen is a crucial protein in the structure and strength of skin, and its synthesis is vital for wound healing. The process involves the assembly of collagen fibers, which requires specific nutritional factors.

## Why the Correct Answer is Right
Vitamin C (ascorbic acid) is essential for the proper assembly of collagen in scar tissue. It acts as a co-factor for the enzymes prolyl hydroxylase and lysyl hydroxylase, which are necessary for the stabilization and cross-linking of collagen molecules. Without vitamin C, collagen synthesis is impaired, leading to weakened connective tissue. This is evident in scurvy, a disease caused by vitamin C deficiency, characterized by poor wound healing and fragile connective tissue.

## Why Each Wrong Option is Incorrect
- **Option A:** While important for overall health, calcium is not directly involved in the assembly of collagen fibers. It plays a critical role in bone health and muscle function but is not a co-factor for collagen synthesis enzymes.
- **Option B:** Although crucial for various bodily functions, including nerve function and the formation of red blood cells, vitamin B12 is not directly involved in collagen assembly.
- **Option D:** Zinc is an essential trace element that plays a role in many aspects of cellular metabolism, including wound healing. However, its primary role is in the regulation of gene expression and as a co-factor for many enzymes, not specifically in the assembly of collagen fibers like vitamin C.

## Clinical Pearl / High-Yield Fact
A key point to remember is that vitamin C deficiency can significantly impair wound healing by affecting collagen synthesis. Clinicians often ensure that patients with wounds or those undergoing surgery have adequate nutrition, including sufficient vitamin C intake, to support the healing process.

## Correct Answer Line
**Correct Answer: C. Vitamin C.**