## Core Concept
The question tests knowledge of ovarian histology, specifically the structure of a Graafian follicle. The PAS (Periodic Acid-Schiff) stain is used to highlight carbohydrate-rich structures, such as glycoproteins and glycolipids, which are abundant in basement membranes and certain cellular components.

## Why the Correct Answer is Right
The bright reddish-pink, acellular ring around the ovum in a Graafian follicle stained with PAS is the **zona pellucida**. This structure is a glycoprotein layer produced by both the oocyte and the follicular cells. It plays a critical role in fertilization, acting as a barrier that must be penetrated by sperm. The zona pellucida's carbohydrate-rich composition makes it strongly PAS-positive, explaining its bright staining.

## Why Each Wrong Option is Incorrect
**Option A:** This option is blank and does not provide a term for consideration.
**Option B:** This option is also blank and does not offer an alternative term.
**Option C:** Similarly, this option is blank and lacks a descriptive term.
**Option D:** This option is blank as well.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **zona pellucida** is crucial for the process of fertilization. Abnormalities or alterations in the zona pellucida can affect fertility. For example, in vitro fertilization (IVF) techniques often involve manipulating or removing the zona pellucida to facilitate embryo implantation.

## Correct Answer Line
**Correct Answer: B. Zona Pellucida**