Explanation: GMDSS regulations for vessels over 300 gross tons operating within range of MF-DSC shore stations (Sea Area A2) mandate that GMDSS equipment be maintained to a certain standard. However, the regulations provide flexibility by offering three distinct maintenance options, of which a vessel needs to implement only one: 1. **Duplication of equipment:** Having redundant critical equipment. 2. **On-board maintenance:** Having a qualified GMDSS Radio Maintainer and appropriate spare parts/test equipment on board. 3. **Shore-based maintenance:** Arranging for service from an approved shore-based maintenance provider. Therefore, only one of these three options is required, making option B correct. Regarding the incorrect options: A) While GMDSS requires continuous watchkeeping on designated distress frequencies (often automated by DSC), it doesn't necessitate the ship's Master or a radio officer to be *manually* on watch at all times. A qualified GMDSS operator must be readily available to handle communications. C) GMDSS communications are typically handled by operators holding a GMDSS Radio Operator's License (GMDSS-RL) or a GMDSS Radio Maintainer's License (GMDSS-RM) with an operator endorsement. While a General Radiotelephone Operator's License (GROL) allows for some GMDSS operation, it is not the *only* or primary required license for all GMDSS functions. D) This statement is too restrictive. If a vessel chooses the duplication or shore-based maintenance options, a comprehensive set of spare parts and a maintenance kit for *all* repairs might not be required on board. It is only specifically mandated for the on-board maintenance option.