**Core Concept**
Collagen is a type of structural protein that forms a strong fibrous structure, providing support and elasticity to various tissues in the body. It is a key component of connective tissue, which includes ligaments, tendons, and aponeuroses.

**Why the Correct Answer is Right**
Fibroblasts are a type of cell that produces collagen and other extracellular matrix components. However, they themselves are not composed of collagen. Instead, they produce collagen as a secreted product, which then becomes an integral part of the surrounding tissue matrix. This distinction is crucial, as fibroblasts are responsible for synthesizing collagen, but they do not contain collagen as a cellular component.

**Why Each Wrong Option is Incorrect**
**Option A:** Ligaments are indeed composed of collagen, which provides their tensile strength and elasticity. Collagen fibers are arranged in a specific pattern to allow for maximum tensile strength while minimizing compressive strength.

**Option B:** Tendons, like ligaments, are also composed of collagen fibers. The unique arrangement of collagen fibers in tendons allows for high tensile strength and resistance to stretch.

**Option D:** Aponeuroses are fibrous sheets of connective tissue that are composed of collagen fibers. They are often found in tendons and ligaments, and play a crucial role in providing stability to joints.

**Clinical Pearl / High-Yield Fact**
Remember that collagen is a key component of connective tissue, and its unique arrangement and composition provide different tissues with distinct mechanical properties. For example, the arrangement of collagen fibers in tendons allows for high tensile strength, while the arrangement in ligaments allows for flexibility and shock absorption.

**Correct Answer:**
✓ Correct Answer: C. Fibroblasts.