RBC that lack nuclei when they are mature are of

Options

A. Frog
B. Lizard
C. Man
D. Birds.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which organism's red blood cells (RBCs) lack nuclei when they are mature.

2. **Identifying RBC Characteristics**: Red blood cells, also known as erythrocytes, are responsible for transporting oxygen throughout the body. In many organisms, RBCs can either have a nucleus or lack one.

3. **Analyzing the Options**: The options provided are:
- Frog
- Lizard
- Man
- Birds

4. **Classifying the Organisms**:
- **Frog**: Frogs are amphibians, and their RBCs are nucleated (they have a nucleus).
- **Lizard**: Lizards are reptiles, and like frogs, their RBCs are also nucleated.
- **Man**: Humans are mammals, and their RBCs are enucleated (they lack a nucleus when mature).
- **Birds**: Birds belong to the class Aves, and their RBCs are nucleated.

5. **Conclusion**: Among the given options, only human RBCs are enucleated when mature. Therefore, the correct answer is **Man**.

**Final Answer**: Man

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