Explanation: GMDSS (Global Maritime Distress and Safety System) compliant battery chargers are critical for ensuring continuous power to vital safety equipment. The specified modes reflect the operational requirements for reliability and redundancy: * **Charging:** This is the primary function, actively replenishing the battery's energy after discharge. * **Change-over:** This mode allows the charger/supply to seamlessly switch between the main AC power source and the backup battery, or between charging the battery and supplying power directly to the GMDSS equipment. This ensures an uninterrupted power supply even if the main power fails. * **Parallel:** In this mode, the charger/supply operates in parallel with the battery, simultaneously providing power to the GMDSS equipment while maintaining the battery's charge. This prevents the battery from discharging under load and provides continuous, stable power. It can also refer to multiple chargers operating in parallel for increased capacity or redundancy. Options B, C, and D describe different stages or methods of charging (float, trickle) or battery states (full), rather than the distinct operational modes of a GMDSS compliant *charger/supply* unit as it interfaces with the system. "Boots" is not a recognized charging term in this context.