In a negative feedback mechanism :

Options

A. the output cancels the input
B. there is a fluctuation above and below the average
C. there is self-regulation
D. a regulatory center communicates with other body parts

Explanation

### Step-by-Step Solution:

1. **Understanding Negative Feedback Mechanism**:
- A negative feedback mechanism is a process in which the output of a system acts to reduce or dampen the processes leading to the output of that system. This means that when a certain function or level is achieved, the system works to bring it back to a set point or average.

2. **Output Cancels Input**:
- In a negative feedback mechanism, the output can indeed cancel the input. For example, if a body temperature rises above normal, the body will initiate processes (like sweating) to cool down, thus canceling the effect of the input (the increase in temperature).

3. **Fluctuation Above and Below Average**:
- The system may experience fluctuations around a set point. For instance, body temperature may rise and fall slightly around the average temperature due to various factors, but the negative feedback mechanism works to keep it within a narrow range.

4. **Self-Regulation**:
- The key feature of a negative feedback mechanism is self-regulation. The system can adjust its output based on the input it receives, maintaining homeostasis. For example, if blood sugar levels rise, insulin is released to lower it, demonstrating self-regulation.

5. **Communication with Regulatory Centers**:
- A regulatory center (like the hypothalamus in the brain) communicates with other body parts to maintain balance. It receives information about the current state of the system and sends signals to effectors to adjust the output accordingly.

6. **Conclusion**:
- In summary, the negative feedback mechanism is characterized by self-regulation, where the output reduces the input, leading to stabilization of the system. Therefore, the correct answer to the question is that there is self-regulation in a negative feedback mechanism.

### Final Answer:
The correct option is C: There is self-regulation in a negative feedback mechanism.

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