RBCs are nucleated in

Options

A. Man
B. Rabbit
C. Rat
D. Frog

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks in which organism red blood cells (RBCs) are nucleated.

2. **Analyzing the Options**:
- **Option 1: Man** - In humans, RBCs are not nucleated. They lose their nucleus during maturation to maximize space for hemoglobin, which carries oxygen.
- **Option 2: Rabbit** - Similar to humans, rabbits also have non-nucleated RBCs.
- **Option 3: Rat** - Rats, like other mammals, have non-nucleated RBCs.
- **Option 4: Frog** - Frogs are amphibians, and their RBCs are nucleated. This is a characteristic feature of amphibians.

3. **Conclusion**: Based on the analysis, the correct answer is that RBCs are nucleated in frogs.

4. **Final Answer**: The correct option is **4. Frog**.