Frog's eye are protected under water by the presence of

Options

A. Retina
B. Upper eyelid
C. Nictitating membrane
D. Lower eyelid

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks how frogs protect their eyes when they are underwater. This requires knowledge of the anatomical structures of a frog's eye.

2. **Analyzing the Options**:
- **Option A: Retina**: The retina is a part of the eye responsible for receiving light and sending visual signals to the brain. It does not provide protection, so this option is incorrect.
- **Option B: Upper Eyelid**: The upper eyelid helps in protecting the eye but does not specifically provide protection when the frog is underwater.
- **Option C: Nictitating Membrane**: This is a special membrane that acts like a protective layer over the eyes, allowing frogs to see while keeping their eyes moist and protected from water.
- **Option D: Lower Eyelid**: Similar to the upper eyelid, the lower eyelid also contributes to eye protection but is not specifically designed for underwater protection.

3. **Identifying the Correct Answer**: Among the options, the nictitating membrane is specifically adapted to protect the eyes of frogs when they are submerged in water. It allows them to see while swimming and protects their eyes from debris and pressure.

4. **Conclusion**: The correct answer to the question is **Nictitating Membrane**.