Explanation: The 121.5 MHz frequency is designated as the international analog distress frequency for homing. While modern 406 MHz satellite EPIRBs transmit precise location data to satellites, they also incorporate a lower-power 121.5 MHz beacon. Search and Rescue (SAR) aircraft and vessels are equipped with specialized direction-finding (DF) equipment tuned to 121.5 MHz. This allows them to "home in" on the signal once they are in the immediate vicinity of the distress, providing the final localization for rescue. The 406 MHz signal (C) is for satellite alerting and position relay to rescue coordination centers, not for direct local homing by nearby vessels. Flare guns (A) and strobe lights (B) are visual distress signals, not radio transmitters, and therefore cannot be used for radio direction finding or homing.