Final answer:
The major advantage of an Incident Command System is that it allows agencies to communicate using common terminology, ensuring clear understanding among various agencies during emergency response.
Step-by-step explanation:
One of the major advantages of an Incident Command System (ICS) is that it allows agencies to communicate using common terminology and operating procedures. The correct answer to this question is A. terminology. The use of standardized terminology is crucial in emergency management contexts where multiple agencies and personnel come together to respond to incidents. This common language ensures that all involved parties understand each other, which is essential for effective coordination and management of emergency situations.