Explanation: Maritime regulations (part of the Global Maritime Distress and Safety System, GMDSS, and enforced by the FCC) specifically mandate that audible alarms for Distress and Urgency DSC messages cannot be disabled by the operator. This is a critical safety feature designed to ensure that life-threatening or serious safety alerts receive immediate and unavoidable attention from watchstanding personnel. A is incorrect because while alarms for lower priority messages (Safety, Routine) can often be silenced, the most critical ones (Distress, Urgency) cannot. B is incorrect; VHF DSC units are required to have both audible and visual alarms. D is incorrect as alarms are typically designed to be distinct for different priorities, especially for Distress, to convey the urgency of the message.