Explanation: When a vessel's Enhanced Group Call (EGC) receiver, part of the GMDSS system, receives SafetyNET Distress or Urgency messages, the system is designed to immediately alert the operator. This is a critical safety function mandated by GMDSS regulations. GMDSS equipment performance standards require that upon receipt of such high-priority messages, both aural (audible) and/or visual alarms are activated. These alarms are designed to persist until manually deactivated by the operator. This ensures the operator's attention is drawn to the critical message and confirms their awareness of its content, preventing vital safety information from being missed. Option A is incorrect because immediate awareness and action are crucial; "no immediate action" is contrary to safety principles. Option B is incorrect because EGC messages are broadcast and do not allow for automatic acknowledgment from the receiving vessel. Option D is incorrect as the alarm typically ceases upon manual deactivation by the operator, confirming awareness, not necessarily just printing the message.