This question belongs to the Class 6 category and requires an explanation of why option D is the correct answer. Let's break down the answer in detail:

Explanation:

1. Understanding the options:
- Option A is not the correct answer because it is missing a response.
- Option B is not the correct answer because it is also missing a response.
- Option C is not the correct answer because it does not provide any specific information or response.
- Option D is the correct answer because it fulfills all the given criteria.

2. Analyzing option D:
- Option D is the correct answer because it is the only option that provides a response to the question.
- The question mark symbol '?' indicates that there is a missing response or information, and option D correctly represents this by providing a placeholder for the missing content.

3. Explanation of the correct answer:
- In this question, the correct answer is option D because it follows the given rules and provides a suitable response to the missing content indicated by the question mark symbol '?'.

Summary:
- In summary, the correct answer to this question is option D because it fulfills all the given criteria by providing a response to the missing content indicated by the question mark symbol '?'.