Explanation: VHF DSC (Digital Selective Calling) operates on a dedicated frequency for digital communications. For VHF radios, this is Channel 70, which is specifically reserved for DSC calls, including distress alerts. When the "Distress Hot Key" is activated, the radio automatically transmits a standardized digital distress message on Ch-70. This ensures that all DSC-equipped vessels and coast stations monitoring Ch-70 immediately receive the digital alert, which includes your vessel's identification and position if a GPS is connected. Options B and C are incorrect because Ch-16 is the international *voice* calling and distress frequency. While voice "MAYDAY" traffic *follows* the DSC alert, the initial digital alert itself is transmitted on Ch-70, not Ch-16. Option D is incorrect because the use of Ch-70 for DSC distress alerts is a mandatory international standard, not dependent on the manufacturer.