What does 10-9 stand for?

• A. Be on the lookout
• B. In service / Available
• C. Acknowledgement
• D. Repeat Last Transmission

Answer: (D)

Understanding radio code usage: when a transmission isn’t heard clearly, you need a quick, unambiguous way to ask for it again. Ten-nine means Repeat Last Transmission. It’s the direct, standard way to request that the previous message be resent so you can catch every detail—location, instructions, numbers, or identifiers—without guessing or guessing. That clarity is why this is the best choice: it communicates the exact action needed without ambiguity.

The other phrases describe different actions you might take on the radio. Be on the lookout signals alert others to a person or vehicle in the area, rather than requesting a repeat. In service or available indicates your status, not something you ask for to clarify a message. Acknowledge or “acknowledgement” is about confirming receipt of a message, not asking for it to be repeated.