Explanation: GMDSS (Global Maritime Distress and Safety System) regulations, enforced under SOLAS (Safety of Life at Sea) convention, mandate robust power arrangements for critical safety equipment. Compulsory ships, typically those engaged in international voyages, are required to have dedicated emergency and reserve power sources for all GMDSS radio installations. This ensures that distress and safety communications can be maintained for a specified duration (e.g., 1 or 6 hours, depending on ship type and battery location) even if the ship's main electrical power supply fails. This dual requirement guarantees operational capability during emergencies. Therefore, A is correct as it accurately reflects this fundamental safety requirement. B is incorrect because both emergency and reserve power capabilities are necessary. While often served by a common battery bank, they represent distinct operational requirements to maintain GMDSS functionality during main power failure. C is incorrect as a reserve power source, typically batteries, is absolutely essential to ensure GMDSS equipment remains operational for a defined period after main power loss. D is incorrect. While a second 406 EPIRB enhances safety, it is a distress alerting device, not a substitute for the comprehensive GMDSS communication systems. The power requirements for the primary GMDSS equipment remain unaffected.