**Core Concept**
Gnarled enamel refers to a specific pattern of enamel development, characterized by irregular and twisted enamel rods. This phenomenon is associated with the morphodifferentiation of enamel, which occurs during tooth development.

**Why the Correct Answer is Right**
The correct answer, C. Cusp tips of tooth, is related to the fact that the cusp tips of teeth exhibit the most pronounced enamel development. During tooth formation, the enamel rods at the cusp tips undergo a process called "enamel knot formation," which leads to the formation of gnarled enamel. This unique pattern is due to the interaction of enamel-producing cells (ameloblasts) with the underlying dentin. The enamel rods at the cusp tips become distorted and twisted, resulting in the characteristic gnarled appearance.

**Why Each Wrong Option is Incorrect**
**Option A:** Proximal surfaces of teeth do not typically exhibit gnarled enamel, as the enamel development in this area is relatively uniform and smooth.
**Option B:** The cervical region of teeth may show signs of enamel wear or erosion, but it is not typically characterized by gnarled enamel.

**Clinical Pearl / High-Yield Fact**
Gnarled enamel is a normal anatomical feature of teeth, particularly at the cusp tips. It is essential to recognize this characteristic during dental examinations and radiographic assessments to avoid misinterpreting it as a pathological or abnormal finding.

**Correct Answer:**
✓ Correct Answer: C. Cusp tips of tooth