Explanation: When a vessel is in distress and unable to contact a Coast Station, any other vessel hearing the distress call has a responsibility to relay it. Since you are already in voice communication on Ch-16, the international voice distress and calling frequency, the most immediate and appropriate action is to relay the distress call using voice. A "Mayday Relay" transmission is the correct procedure for a voice relay of a distress message, ensuring other vessels or a Coast Station are alerted on the appropriate voice channel with the highest priority. A) Sending a DSC Distress Relay on Ch-16 is incorrect. Ch-16 is for voice communications; DSC (Digital Selective Calling) transmissions are typically made on Ch-70, the dedicated DSC calling channel, not Ch-16. C) Making an all ships call with Urgency (Pan-Pan) priority is insufficient. The vessel is in Distress (Mayday), which is a higher priority than Urgency, requiring a "Mayday Relay." D) Calling the Coast Station on Ch-70 with Distress priority using voice is incorrect. Ch-70 is the DSC calling channel and is primarily used for digital selective calling, not for voice communication.