Explanation: Upon receiving a VHF Distress alert via Digital Selective Calling (DSC) on Ch-70, the immediate priority after silencing the alarm is to establish a listening watch on the designated voice distress frequency. **Why D is Correct:** * **Silence the alarm:** This is the initial logical step to stop the audible alert and focus attention. * **Set up watch on Ch-16:** VHF Ch-70 is exclusively for DSC alerting. All follow-up voice communications for distress, urgency, and safety traffic must take place on VHF Ch-16 (156.8 MHz), the international distress and calling frequency. This is a fundamental regulation in maritime radio operations. * **To determine if the Distress is genuine:** Listening on Ch-16 allows you to hear the actual voice distress message, assess the situation, and determine if your vessel can render assistance or relay the information. **Why others are incorrect:** * **A) Call the Master to verify...:** While informing the Master is essential, the immediate action should be to monitor the distress channel; verification comes from listening to the voice traffic. * **B) Acknowledge the DSC alert via DSC:** A vessel receiving a distress alert from another vessel should *not* acknowledge it via DSC. This could potentially block others from acknowledging or responding. Acknowledgement via DSC is primarily for Coast Stations/Rescue Coordination Centers. Vessels should listen on Ch-16 and acknowledge by voice, or contact an RCC if they can provide assistance. * **C) Listen for any follow on voice transmission on Ch-70:** This is incorrect. Ch-70 is a DSC-only channel; voice transmissions are strictly prohibited on Ch-70. All voice follow-up for distress is on Ch-16.