On an Inmarsat-C system an alarm sounds:

Correct Answer: Option B — When receiving Distress traffic.

The Inmarsat-C terminal is a critical component of the GMDSS. It is programmed to trigger an audible alarm specifically when it receives high-priority distress traffic or urgent maritime safety information. This ensures that the bridge watch is immediately alerted to life-critical situations, even if the terminal is not being actively monitored.