When operating in coastal waters (sea area A1), a GMDSS-equipped vessel must:

Correct Answer: Option D — Maintain a continuous DSC watch on VHF channel 70.

Sea Area A1 is defined by SOLAS as the radiotelephone coverage area of at least one VHF coast station in which continuous digital selective calling alerting is available, requiring continuous DSC watchkeeping specifically on VHF channel 70.