Explanation: Sending a brief message to your own Inmarsat-C terminal is the most effective test because it constitutes a complete loop-back test. This verifies the entire operational chain: your terminal's ability to transmit the message to the satellite, the satellite's relay to the Land Earth Station (LES), the LES processing and routing the message, and finally, your terminal's ability to successfully receive and decode the message returning via the satellite. This confirms both transmit and receive functionality, along with proper network connectivity and configuration for your specific device. Other options are less comprehensive: sending to a shore or another ship terminal only confirms your transmit path and network connectivity *to* them; it doesn't inherently confirm your receive capability without a specific reply. A flashing "Send" light only indicates a transmit attempt, not successful delivery or the terminal's receive functionality.