The correct answer is C) Switch on EPIRB and SART immediately and leave on. In a distress situation where the crew is abandoning the vessel, the priority is to activate the Emergency Position-Indicating Radio Beacon (EPIRB) and Search and Rescue Transponder (SART) immediately upon entering the survival craft. This will alert the Rescue Coordination Center (RCC) to the vessel's distress and provide a homing signal for search and rescue teams to locate the survival craft. Leaving the EPIRB and SART powered on is crucial, as it allows the distress signal to continue being transmitted even if the vessel is lost or submerged. The other options are incorrect because: A) using the VHF DSC may not be possible if the vessel is already abandoned, B) communicating via Inmarsat-C requires additional equipment that may not be available in the survival craft, and D) manually activating the EPIRB and SART prior to launching may delay the distress signal and reduce the chances of a timely rescue.