The correct answer is option 'D' - Trading Posts.

Explanation:
Trading posts are the posts on the floor of the stock exchange where traders and brokers gather to buy and sell securities. These posts serve as physical locations where the trading activity takes place. Here is a detailed explanation of trading posts and their significance in the stock exchange:

1. Definition of Trading Posts:
- Trading posts are designated areas on the floor of the stock exchange where traders and brokers conduct transactions.
- These posts are typically marked by physical structures or designated areas where traders gather to execute trades.

2. Function of Trading Posts:
- Trading posts provide a centralized location for traders to meet and interact with each other.
- Traders gather at these posts to buy and sell securities, negotiate prices, and execute trades.
- The open outcry method, where traders shout and use hand signals to communicate, is often employed at these posts.

3. Significance of Trading Posts:
- Trading posts play a crucial role in facilitating the exchange of securities.
- They provide a physical space where buyers and sellers can come together and establish market prices through supply and demand.
- The interaction between traders at these posts helps determine the current market price of securities.
- Trading posts also serve as a visible representation of the stock exchange, where the hustle and bustle of trading activity can be witnessed.

4. Evolution of Trading Posts:
- With the advent of electronic trading systems, the importance of trading posts has diminished.
- Many stock exchanges now rely heavily on computerized trading platforms, where trades are executed electronically.
- However, in some exchanges, trading posts still exist, especially for certain types of securities or specialized trading activities.

In conclusion, trading posts are the designated areas on the floor of the stock exchange where traders and brokers gather to buy and sell securities. While their significance has diminished with the rise of electronic trading systems, these posts still play a role in facilitating face-to-face trading interactions and establishing market prices.