**Core Concept**
The question requires knowledge of the distribution of hydroxyproline, a non-essential amino acid that is crucial for the synthesis of collagen, a primary structural protein found in connective tissue. Hydroxyproline is formed from proline through a hydroxylation reaction catalyzed by prolyl hydroxylase.

**Why the Correct Answer is Right**
The correct answer is related to the fact that collagen is the most abundant protein in the human body, particularly in skin, bones, tendons, and ligaments. Hydroxyproline is essential for the stabilization of collagen's triple-helix structure, which provides tensile strength to these tissues. The highest concentration of hydroxyproline is found in skin, where it constitutes approximately 12-14% of the total amino acid content.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while hydroxyproline is present in muscles, its concentration is not the highest among all tissues.
**Option B:** Incorrect because although hydroxyproline is found in bones, its concentration is not as high as in skin.
**Option C:** Incorrect because while hydroxyproline is present in tendons and ligaments, its concentration is not the highest among all tissues.

**Clinical Pearl / High-Yield Fact**
Remember that hydroxyproline is a key indicator of collagen turnover and can be measured in the urine to assess bone resorption and collagen metabolism.

**Correct Answer:** C. Skin.