To ensure control, units sending radio messages must:

• A. Repeat code 10-4 after each transmission
• B. Include an acknowledgement specific to their department
• C. Identify who they are calling and identify themselves before transmitting their message
• D. Identify themselves and reply, "understood"

Answer: (C)

Clear, effective radio control starts with establishing both sides of the conversation before you say a word. By identifying who you are calling and identifying yourself, you set the exact target of the transmission and the originator of the message. This creates immediate context for the listener, helps ensure the message reaches the right unit on a potentially busy channel, and provides accountability for who is communicating. It also supports proper command and coordination on the scene, where rapid, accurate exchanges are crucial.

Other options introduce unnecessary chatter or don’t ensure the right recipient or sender is known. Repeating a generic acknowledgement after every transmission wastes time and may not be universally understood. Requiring department-specific acknowledgments isn’t standard across all agencies and can slow operations. Forcing a reply of “understood” doesn’t reliably confirm who is listening or who is speaking, and it doesn’t establish who is on the call.