Explanation: Portable survival craft transceivers are designated for emergency communication during distress incidents. Their fundamental purpose is to facilitate rescue and coordination. * **A) Communication is permitted between survival craft:** This allows occupants of multiple survival craft to coordinate their actions, share information, and potentially stay together for rescue, enhancing overall safety. * **B) Communication is permitted between survival craft and ship:** This is crucial for initial rescue efforts, allowing the survival craft to communicate with vessels in the vicinity, including their mother ship if still afloat, or other ships responding to distress calls. * **C) Communication is permitted between survival craft and rescue unit:** Direct communication with dedicated search and rescue (SAR) units (e.g., Coast Guard vessels, aircraft) is paramount for precise location, status updates, and successful extraction. All these communication pathways are essential for an effective rescue operation, making communication with any of these entities permissible and indeed, the intended use for these critical safety devices.