In a healthy adult man, the smallest type of leucocytes are

Options

A. Basophils
B. monocytes
C. eosinophils
D. lymphocytes

Explanation

To determine the smallest type of leucocytes (white blood cells) in a healthy adult man, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Types of Leucocytes**:
- Leucocytes are classified into two main categories: granulocytes and agranulocytes. Granulocytes include basophils, eosinophils, and neutrophils, while agranulocytes include lymphocytes and monocytes.

2. **List the Options**:
- The options provided are:
- A) Basophil
- B) Monocyte
- C) Eosinophil
- D) Lymphocyte

3. **Understand the Size Order of Leucocytes**:
- Generally, the size of leucocytes can be ordered as follows:
- Monocytes (largest)
- Eosinophils
- Basophils
- Lymphocytes (smallest)

4. **Analyze the Options**:
- From the size order, we can see that:
- Monocytes are the largest.
- Eosinophils are larger than lymphocytes but smaller than monocytes.
- Basophils are smaller than eosinophils but larger than lymphocytes.
- Lymphocytes are the smallest type of leucocytes.

5. **Conclusion**:
- Based on the analysis, the smallest type of leucocytes in a healthy adult man is **Lymphocyte**.

### Final Answer:
The smallest type of leucocytes in a healthy adult man is **Lymphocyte (Option D)**.

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