Explanation: Under GMDSS regulations, a ship's primary purpose for its communication equipment is to ensure safety of life at sea, especially during distress situations. **C) The vessel is not capable of performing all required Distress and Safety functions.** This is the correct answer because GMDSS mandates that a ship must be fully operational in its communication capabilities to ensure it can send and receive distress alerts, transmit maritime safety information, and perform general communications necessary for safety. If a vessel cannot perform these critical functions, it poses an unacceptable risk and is not permitted to depart port. This directly violates the fundamental safety purpose of GMDSS. **A) The vessel is carrying more than the required number of qualified GMDSS radio operators.** Carrying extra qualified personnel is a safety advantage, not a reason to prevent departure. **B) The vessel has a temporary waiver of its radio license and Safety Certificate.** While not ideal, a temporary waiver can be issued under specific, limited circumstances (e.g., equipment failure en route to a repair port), often with compensatory measures and flag state approval. Thus, it does not *always* prevent departure. **D) The vessel is not carrying a GMDSS radio maintainer, but has provided for shoreside maintenance plus...** GMDSS allows for different maintenance options. A vessel is not required to carry a dedicated maintainer if it has opted for shoreside maintenance *in conjunction with* either duplication of critical equipment or specific equipment-at-sea maintenance strategies. This is a permissible arrangement.