What is the purpose of depressing the button on the handle of a sound-powered telephone handset?

Correct Answer: Option A — The button must be depressed to speak and to listen.

The button on a sound-powered telephone handset acts as a push-to-talk switch that completes the circuit for both transmission and reception. It must be held down during the entire conversation to ensure the circuit remains active, allowing for clear two-way communication between the bridge and the engine room.