Explanation: The Dual Watch (DW) function on a marine VHF radio is a critical safety feature designed to ensure compliance with the requirement to monitor Channel 16, the international distress, safety, and calling frequency. It allows you to select a working channel for general communication (e.g., ship-to-ship, weather, harbor operations) while the radio periodically and briefly switches to Channel 16 to listen for any calls. If activity is detected on Channel 16, the radio will stay on that channel, alerting the user to a distress call or another vessel attempting to make contact. This prevents missing crucial safety broadcasts or calls while engaged in other communications. * **A) Listen to Ch-70 at the same time while monitoring Ch-16.** Is incorrect. While modern DSC radios continuously monitor Ch-70 (Digital Selective Calling) in the background, this is a separate, digital function of the DSC controller, not the voice-oriented Dual Watch function. Dual Watch focuses on voice monitoring of a working channel and Ch-16. * **B) Sequentially monitor 4 different channels.** Is incorrect. This describes a standard scanning function, not the specific purpose of Dual Watch, which prioritizes a working channel and Ch-16. * **C) Sequentially monitoring all VHF channels.** Is incorrect. This describes a full scan function, not Dual Watch, which is a specialized priority monitoring mode.