Explanation: GMDSS regulations mandate that vessels must be able to receive Maritime Safety Information (MSI) continuously. In coastal areas, this is typically provided by NAVTEX. However, when operating outside of NAVTEX coverage, an alternative system is required. The Inmarsat Enhanced Group Call (EGC) system, specifically SafetyNET, is the GMDSS-mandated satellite service for broadcasting MSI to vessels operating in sea areas beyond NAVTEX range. Therefore, a GMDSS-equipped vessel in Ocean Area A1 that is outside NAVTEX coverage must carry equipment (typically an Inmarsat-C terminal) capable of receiving MSI via the Inmarsat EGC system to fulfill this critical safety requirement. * **B) A GPS receiver:** While essential for navigation and providing position data to GMDSS equipment, a GPS receiver does not provide MSI itself. * **C) Equipment capable of maintaining a continuous DSC watch on 2187.5 kHz:** The 2187.5 kHz DSC frequency is for MF band communications, primarily required for vessels operating in Ocean Area A2 and beyond. Vessels operating *only* in Ocean Area A1 are primarily required to maintain a VHF DSC watch on Channel 70. * **D) An Inmarsat-B terminal:** Inmarsat-B provides voice, telex, and data services but is not the *mandated* or standard system for MSI reception under GMDSS; the Inmarsat EGC system (often integrated into Inmarsat-C terminals) is specified for this purpose.