Setae help in locomotion in earthworm but are not uniformly present in all the segments. They are present in

Options

A. `1^(st)` segment
B. last segment
C. Clitellar segment
D. `20^(th)-22^(nd)` segment

Explanation

To answer the question regarding the presence of setae in earthworms, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Setae**: Setae are small, bristle-like structures found on the body of earthworms. They are made of chitin and play a crucial role in locomotion by anchoring the worm to the ground as it moves.

2. **Identifying the Segments**: Earthworms have a segmented body plan. Each segment can have different structures, including setae.

3. **Segments Without Setae**: It is important to note that setae are not uniformly present in all segments. Specifically, setae are absent in:
- The first segment (prostomium)
- The last segment (anus)
- The clitellar segments (segments 14, 15, and 16)

4. **Segments With Setae**: Setae are present in most of the other segments of the earthworm's body, particularly from segment 20 to segment 22, where they assist in locomotion.

5. **Conclusion**: Therefore, the segments where setae are present are from segment 20 to segment 22, while they are absent in the first segment, last segment, and the clitellar segments.

### Final Answer:
Setae are present in segments 20 to 22 of the earthworm.