Explanation: When the primary NAVTEX receiver is inoperative, GMDSS regulations require a secondary means of receiving Maritime Safety Information (MSI). NAVTEX broadcasts on 518 kHz. The designated backup for a failed NAVTEX receiver, particularly when within NAVTEX coverage, is to use the vessel's MF/HF radio to receive Narrow Band Direct Printing (NBDP) broadcasts on the same 518 kHz frequency. Forward Error Correction (FEC) TELEX mode is the appropriate choice for this one-way broadcast reception, as it's designed for reliable reception even with some errors, without needing a return channel. Option B is incorrect because ARQ (Automatic Repeat Request) TELEX is a two-way, point-to-point communication protocol requiring acknowledgements, which is unsuitable for receiving one-way broadcast MSI. Option C is incorrect because waiting for repairs or until within range is not an immediate solution for vital safety information; GMDSS mandates an active alternative. Option D is incorrect because while HF can carry MSI, the direct backup for the 518 kHz NAVTEX is MF NBDP on the same 518 kHz frequency. Also, ARQ is the wrong mode for broadcast reception.