Which of the following is a primary lymphoid organ ?

Options

A. Pancreas
B. Liver
C. Kidney
D. Thymus

Answer

To determine which of the following is a primary lymphoid organ, we need to understand the definitions and functions of primary and secondary lymphoid organs.

### Step-by-Step Solution:

1. **Understand Lymphoid Organs**: Lymphoid organs are crucial components of the immune system and are divided into two categories: primary lymphoid organs and secondary lymphoid organs.

2. **Identify Primary Lymphoid Organs**: Primary lymphoid organs are where lymphocytes (a type of white blood cell) are produced and mature. The two main primary lymphoid organs are:
- **Bone Marrow**: This is where B-cells are formed and mature.
- **Thymus**: This is where T-cells are formed in the bone marrow but mature in the thymus.

3. **Evaluate the Options**:
- **Pancreas**: This organ is primarily involved in digestion and is not a lymphoid organ.
- **Liver**: The liver plays a role in metabolism and detoxification, not in lymphocyte maturation.
- **Kidney**: The kidneys are excretory organs and do not function as lymphoid organs.
- **Thymus**: This is a primary lymphoid organ where T-cells mature.

4. **Conclusion**: Based on the definitions and functions of the organs listed, the correct answer is **Thymus**, as it is a primary lymphoid organ.

### Final Answer:
**Thymus** is the primary lymphoid organ among the given options.

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