Explanation: On-scene communications, particularly for distress, urgency, or safety, are typically initiated using VHF Channel 16. This is the international voice calling and distress frequency for maritime VHF radio. It is continuously monitored by the Coast Guard and other vessels, making it the primary channel for making initial contact in an emergency or for coordinating actions between vessels. * **A) EPIRB on 121.5 MHz:** An EPIRB (Emergency Position-Indicating Radio Beacon) transmits a distress signal to satellites (primarily 406 MHz, with 121.5 MHz as a homing frequency for older units) to alert search and rescue authorities. It does not provide two-way voice communication for on-scene coordination. * **B) SART on 9 GHz:** A SART (Search and Rescue Transponder) is a device that responds to marine radar signals (9 GHz X-band radar) from search vessels, helping them locate a survival craft. It's a locating aid, not an initiating communication device. * **D) VHF on Ch-70:** Channel 70 is dedicated exclusively to Digital Selective Calling (DSC). While it's used to *initiate* a digital distress alert or call, the subsequent voice communication would then shift to a working channel, often Channel 16 or another designated channel. The question implies initial voice contact for on-scene coordination.