**Core Concept**
Collagen is the most abundant protein in the human body, forming a strong scaffold for connective tissue. It is composed of a unique amino acid sequence that provides its remarkable strength and elasticity. Specifically, collagen contains a high proportion of amino acids with specific functional groups that facilitate cross-linking and stabilization of the triple helix structure.

**Why the Correct Answer is Right**
Collagen is characterized by an abundance of amino acids with hydroxy groups, such as **hydroxyproline** and **hydroxylysine**. These amino acids are essential for the formation of stable cross-links between collagen molecules, which is critical for the development and maintenance of connective tissue. The presence of these amino acids also allows collagen to interact with other molecules, such as glycosaminoglycans, to form a complex extracellular matrix.

**Why Each Wrong Option is Incorrect**
**Option A:** Glycine is indeed a key component of collagen, but it is not the most distinctive or characteristic amino acid in the collagen sequence. Glycine is present in every third position in the collagen triple helix, providing a compact and stable structure.
**Option B:** Alanine is a non-essential amino acid that is present in many proteins, but it is not specifically characteristic of collagen. While collagen does contain some alanine residues, they are not as abundant as hydroxyproline and hydroxylysine.
**Option C:** Arginine is a positively charged amino acid that plays a role in many biological processes, but it is not a key component of collagen. While collagen does contain some arginine residues, they are not as important for its structure and function as hydroxyproline and hydroxylysine.

**Clinical Pearl / High-Yield Fact**
When considering the structure and function of collagen, remember that the presence of hydroxyproline and hydroxylysine is critical for the formation of stable cross-links between collagen molecules. This is why these amino acids are often used as biomarkers for collagen synthesis and degradation in clinical and research settings.

**Correct Answer:** C.