Explanation: GMDSS (Global Maritime Distress and Safety System) regulations prioritize the continuous availability of essential communication equipment. To achieve this, ships are given flexibility in how they maintain their systems. * **Shore Maintenance (A):** This involves relying on qualified personnel at port to repair equipment, often with pre-arranged service contracts. * **Duplication of Equipment (B):** For critical systems, having a complete backup unit ensures that if one fails, the other can immediately take over, maintaining operational capability. * **At Sea Maintenance (C):** This means the ship's crew, specifically a qualified radio officer or maintainer, performs repairs using onboard spare parts and testing equipment while underway. The regulations (SOLAS Chapter IV) state that a vessel can fulfill its GMDSS maintenance obligations by choosing *any one* of these three methods. There is no requirement to implement all of them simultaneously. Therefore, demonstrating compliance with any one of these provisions is sufficient.