**Core Concept**
The question is testing knowledge of the anatomy of the lens in the eye, specifically the arrangement of old and new fibers. The lens is composed of layers of cells, with old fibers located in the central part of the lens and new fibers located in the periphery.

**Why the Correct Answer is Right**
The correct answer is related to the process of lens growth and development. As the lens grows, new cells are added to the periphery, while old cells are pushed towards the center, forming a layered structure. This process is essential for maintaining the lens's refractive power and transparency. The old fibers in the center of the lens are compact and densely packed, contributing to the lens's refractive power.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the epithelial cells are located in the anterior (front) part of the lens, not the region where old fibers are located.
**Option B:** This option is incorrect because the zonular fibers are part of the suspensory ligament that supports the lens, not the location of old fibers.
**Option C:** This option is incorrect because the lens capsule is the outermost layer of the lens, not the region where old fibers are located.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lens's layered structure is responsible for its refractive power, and any disruptions to this structure, such as cataract formation, can lead to vision loss.

**Correct Answer: C. The nucleus.**