Explanation:

The correct answer is option 'B', which is the Zona pellucida. Let's understand why.

Zona pellucida:
- The zona pellucida is a glycoprotein layer that surrounds the oocyte (immature egg) in the ovary.
- It is a thick, transparent layer that plays a crucial role in fertilization and early embryonic development.
- The zona pellucida is produced by the oocyte itself and is composed of several glycoproteins, including ZP1, ZP2, and ZP3.

Function of the Zona pellucida:
1. Protection: The zona pellucida acts as a protective barrier around the oocyte, preventing mechanical damage and protecting it from the external environment.
2. Sperm binding: The glycoproteins present in the zona pellucida have specific binding sites for sperm. This allows the sperm to attach to the zona pellucida and initiate the process of fertilization.
3. Species-specific barrier: The zona pellucida provides a species-specific barrier, meaning that it only allows sperm of the same species to bind and penetrate. This helps in maintaining reproductive isolation between different species.
4. Acrosome reaction: When sperm bind to the zona pellucida, it triggers the acrosome reaction. This is a series of biochemical changes in the sperm that allow it to penetrate the zona pellucida and reach the oocyte for fertilization.
5. Prevention of polyspermy: After the entry of the first sperm, the zona pellucida undergoes a hardening process called the zona reaction, which prevents the entry of additional sperm. This is essential to ensure that only one sperm fertilizes the oocyte, as polyspermy (fertilization by multiple sperm) can lead to abnormal embryonic development.

Other layers:
- Theca externa: It is the outermost layer of the ovarian follicle and is primarily composed of connective tissue.
- Membrana granulosa: It is the layer of cells that surrounds the oocyte within the follicle.
- Vitelline membrane: It is a membrane that surrounds the egg yolk in some animals, but it is not present in humans.

Therefore, the glycoprotein layer is the zona pellucida, which is option 'B' in the given options.