When part of a message has been received and the rest needs repeating, which term is most appropriate to use?

The term that is most appropriate to use when part of a message has been received and the rest needs repeating is "Repeat." This term clearly communicates to the sender that they should resend the message, allowing the receiver to obtain all necessary information without ambiguity. Using "Repeat" establishes an expectation for clarity and thoroughness in communication, which is essential in situations that require precise instructions or information, such as in public safety communications.

The other terms do not accurately convey the need for a message to be repeated. "Affirmative" typically indicates understanding or agreement rather than a request for further information. "Busy" would imply that the communication line is occupied and not available for further messages, while "In service" suggests that a system or unit is operational but does not instruct for message repetition. Therefore, "Repeat" is the best choice, as it directly addresses the need for clarification and the continuation of the communication flow.