Explanation: Equipment for radiotelephony (voice) use in survival craft under GMDSS (Global Maritime Distress and Safety System) must be capable of operating on VHF Channel 16 (156.8 MHz). Ch-16 is the internationally recognized voice distress, safety, and calling frequency for maritime communications. It ensures that survival craft can communicate directly with ships, coast stations, and rescue assets monitoring the channel. Operation on 457.525 MHz (A) is not a designated GMDSS voice distress frequency. 121.5 MHz (C) is an aviation distress frequency, primarily for ELTs (Emergency Locator Transmitters), not for maritime voice communication. Channel 70 (D) is the dedicated frequency for DSC (Digital Selective Calling) distress alerts, which transmits digital data, not radiotelephony (voice).