Explanation: Passenger vessels are specifically required to carry an aeronautical survival craft two-way radiotelephone apparatus operating on the international aeronautical distress frequency of 121.5 MHz (and often 123.1 MHz). This crucial equipment enables direct voice communication between survivors in distress (e.g., in lifeboats) and search and rescue (SAR) aircraft overhead, significantly enhancing the effectiveness and speed of rescue operations. The other options are incorrect as they serve different purposes. Inmarsat-B and Inmarsat-C terminals are satellite communication systems primarily used within the Global Maritime Distress and Safety System (GMDSS) for distress alerting, safety, and general communication with shore stations or other vessels. An MF-HF SSB transceiver is also a GMDSS component for long-range voice and Digital Selective Calling (DSC) communications, but none of these facilitate direct, line-of-sight communication with SAR aircraft on their dedicated emergency frequencies.