Final answer:
The key principle that involves the use of familiar communications and information systems is Interoperability, which enables different systems to work together effectively.
Step-by-step explanation:
The use of communications and information systems that are familiar to users is a part of the key principle: A. Interoperability. This principle ensures that different systems and organizations can work together (inter-operate) effectively. Interoperability is vital in various fields, including emergency services, military operations, and healthcare, where it is essential for different systems and pieces of equipment to communicate and work together seamlessly to achieve a common goal.