The correct answer is **b. iterative prototyping** and also **d. divide and conquer**, but mostly **b. iterative prototyping**. 

Here's why:
* **Iterative Prototyping** is a key concept in Agile Methodology, which involves breaking down a complex system into smaller, manageable parts, and then iteratively refining and improving the design through continuous testing and feedback. This approach is often used in software development and is a good fit for **Structure Design**.
* **Divide and Conquer** is a problem-solving strategy that involves breaking down a complex problem into smaller, more manageable sub-problems, solving each sub-problem, and then combining the solutions to solve the original problem. While this approach can be used in structure design, it is not as closely tied to Agile Methodology as Iterative Prototyping.

The other options are not as relevant to structure design:
* **Agile Methodology** is a broader concept that encompasses a range of values, principles, and practices for software development, including iterative prototyping, continuous improvement, and customer collaboration.
* **Top-Down Parsing** is a parsing technique used in compiler design, which involves analyzing the syntax of a programming language from the top level (i.e., the overall structure of the program) down to the individual symbols and tokens.

So, to summarize:
* **b. iterative prototyping** is the most relevant answer, as it is a key concept in Agile Methodology and is often used in structure design.
* **d. divide and conquer** is also a relevant answer, as it is a problem-solving strategy that can be applied to structure design.
* **a. agile methodology** is too broad, and **c. top-down parsing** is not directly related to structure design.