Explanation: GMDSS regulations allow for a flexible approach to equipment maintenance, ensuring the availability of essential communication systems on vessels. For A3 ships, operating far from shore, robust maintenance strategies are critical. **Correct Answer Explanation:** **C) Redundancy of functions of certain equipment and on-board maintenance provided by a person holding a GMDSS Maintainer's license will fully meet the requirement.** GMDSS regulations (SOLAS Chapter IV, Regulation 15) allow for maintaining the availability of equipment through one or a combination of three methods: duplication of equipment (redundancy), on-board maintenance by a qualified GMDSS Maintainer, or shore-based maintenance. This option describes a robust and commonly adopted combination of two of these methods. Redundancy ensures critical functions remain available even if a primary unit fails, while an on-board maintainer allows for prompt repairs at sea, ensuring high availability in remote areas. **Incorrect Answer Explanations:** **A) If the vessel selects at-sea maintenance no additional parts and spares are required.** This is incorrect. Regardless of the maintenance strategy, adequate spares and test equipment are always required to perform effective repairs and ensure the continued functionality of GMDSS equipment. **B) On-board maintenance provided by a person holding a GMDSS Maintainer's license will fully meet the requirement.** While on-board maintenance by a licensed individual is one of the accepted methods, it may not be sufficient on its own for all A3 vessels depending on the specific equipment and flag state requirements. Option C describes a more comprehensive and often preferred combined approach for ensuring high reliability. **D) Shoreside maintenance and scheduled tests and inspections will not partially meet this requirement.** This is incorrect. Shoreside maintenance is one of the three recognized methods for ensuring GMDSS equipment availability. While it might be impractical as the sole method for an A3 ship far from shore, it certainly *can* partially meet or be a component of the overall maintenance strategy.