Explanation: A compulsory vessel must ensure all critical safety equipment, especially GMDSS (Global Maritime Distress and Safety System) apparatus, is fully functional and verified before leaving port. If a required piece of GMDSS equipment has been replaced but its performance has not been adequately checked or confirmed to the satisfaction of the master, the vessel's ability to communicate in an emergency is compromised. International regulations (SOLAS) and national rules mandate the operational readiness of GMDSS for vessel safety. An unverified or malfunctioning system poses an unacceptable risk, preventing departure. Option B refers to cargo issues, not directly related to radio equipment readiness. Option C describes a legitimate and compliant GMDSS maintenance strategy (duplication and shore-based maintenance), which would *allow* a vessel to sail, not prevent it. Option D describes a vessel that is likely compliant with GMDSS manning requirements, as two licensed operators are often sufficient to maintain watch and perform all necessary communication functions.