Which action must be taken to ensure that incoming message traffic of all priority levels will be received through Inmarsat-C?

Correct Answer: Option C — The GMDSS Radio Operator must log-in to the desired satellite.

Inmarsat-C terminals operate in a store-and-forward mode. To receive incoming messages, the terminal must establish a handshake with the network. Logging in to the specific satellite serving the current ocean region is the mandatory operational step to register the terminal's presence and enable the reception of all priority traffic.