To solve the problem, we need to understand the key characteristics of individual agents in a multi-agent system (MAS). Let's evaluate each option:

1. Statement A: "They must be identical in their capabilities and goals."
   • This statement is incorrect. In a multi-agent system, agents do not need to be identical. They can have different capabilities, goals, and roles within the system. Diversity among agents allows the system to tackle complex tasks that a single agent type could not handle effectively.
2. Statement B: "They are autonomous and act independently."
   • This is a correct statement. Agents in a multi-agent system operate independently and can make their own decisions based on their programming or learning algorithms. Autonomy is a fundamental characteristic of agents in these systems.
3. Statement C: "They interact with each other and their environment."
   • This is correct. Agents in a multi-agent system frequently interact with both the environment they operate within and other agents. Such interactions can be cooperative, competitive, or neutral and are essential for achieving collective tasks or coordinating actions.
4. Statement D: "They are controlled by a single, centralized authority at all times."
   • This statement is incorrect. The essence of a multi-agent system is decentralization, where agents do not rely on a central authority for decision-making and control. Instead, they work based on local information and interactions.

Based on the above analysis, the correct characteristics of agents in a multi-agent system are observed in statements B and C. Therefore, the correct answer is the option that includes B and C, and since statement A is not characteristic of agents, we dismiss it. Hence, considering these, the correct choice is: A, B & C Only

Thus, the selected option correctly reflects the characteristics of agents in a multi-agent system where they are autonomous, interact with each other and their environment, and are not required to be identical.