Which is a primary lymphoid organ

Options

A. Bone marrow and spleen
B. Spleen and thymus
C. Bone -marrow and tonsils
D. thymus gland and bone marrow

Answer

To answer the question "Which is a primary lymphoid organ?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Primary Lymphoid Organs**:
- Primary lymphoid organs are those where lymphocytes (B and T cells) are formed and mature.

2. **Identify the Primary Lymphoid Organs**:
- The two primary lymphoid organs are:
- **Bone Marrow**: This is where B cells mature and where all lymphocytes are produced.
- **Thymus Gland**: This is where T cells mature.

3. **Analyze the Options Given**:
- The options provided are:
- A) Bone marrow and spleen
- B) Spleen and thymus
- C) Bone marrow and tonsils
- D) Thymus gland and bone marrow
- From our understanding, we know that:
- Spleen and tonsils are secondary lymphoid organs.
- Therefore, options A, B, and C are incorrect.

4. **Select the Correct Option**:
- The only option that includes both primary lymphoid organs (bone marrow and thymus) is option D: **Thymus gland and bone marrow**.

5. **Conclusion**:
- The correct answer to the question is **Thymus gland and bone marrow**.

### Final Answer:
**Thymus gland and bone marrow**

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