Explanation: Proper watchkeeping in a GMDSS (Global Maritime Distress and Safety System) environment requires an operator to be fully aware of the station's status and any incoming alerts. When an alarm sounds, it signifies an event that needs immediate attention. Silencing the alarm is the first step, but it must be followed by thoroughly reading all displays and printouts to understand the nature of the alert (e.g., distress, urgency, safety, equipment fault). Additionally, maintaining a continuous watch involves monitoring *all required frequencies* (such as VHF Ch 70 DSC, MF 2187.5 kHz DSC, and appropriate HF DSC frequencies, along with associated voice channels) *in the correct mode* (e.g., DSC or R/T) to ensure all calls are received. Options B, C, and D are incorrect because they provide incomplete or inaccurate information regarding mandatory DSC watch frequencies. The mandatory DSC watch includes VHF Channel 70 and MF 2187.5 kHz, with HF DSC watch typically encompassing frequencies like 4 MHz, 6 MHz, 8 MHz, 12 MHz, and 16 MHz depending on the sea area. Options B and C's specification of "2 MHz, 4 MHz and 8 MHz" for the DSC scanner is incomplete, notably omitting VHF Ch 70 and other crucial HF frequencies. Option D incorrectly states "only to the mandatory 2 MHz & 8 MHz" and misplaces continuous watch emphasis on 2182.0 kHz voice instead of the mandatory 2187.5 kHz DSC for GMDSS vessels.