Introduction:
Setae are small bristle-like structures that are present on the body segments of certain organisms. These structures serve various functions such as locomotion, sensing, and attachment. In this question, we are asked to identify the segment in which setae are present.

Explanation:
To determine the segment in which setae are present, let's analyze each option provided.

a) First segment:
The first segment of an organism's body is usually specialized for a specific function and may not have setae. For example, in earthworms, the first segment is called the prostomium, which is a sensory structure that lacks setae.

b) Second segment:
The second segment of an organism's body is often the first true body segment. In earthworms, this segment is called the peristomium, and it does possess setae. The setae in this segment help in locomotion and anchoring the worm.

c) Clitellar segments:
The clitellum is a specialized glandular region found in certain annelids, including earthworms. It is responsible for producing the cocoon during reproduction. While the clitellar segments play a crucial role in reproduction, they do not typically have setae.

d) Last segment:
The last segment of an organism's body may vary in structure and function. In earthworms, the last segment is called the pygidium, which is primarily involved in excretion. It does not possess setae.

Conclusion:
Based on the analysis, it can be concluded that setae are present in the second segment of the organism's body. This is the correct answer option 'B'. The presence of setae in this segment aids in locomotion and attachment.