Explanation: Channel 26 (Ch-26) is a designated Marine VHF voice channel specifically allocated for **duplex communications**. In the Marine VHF service, duplex channels use separate frequencies for transmitting and receiving, allowing for simultaneous two-way conversations, primarily between a vessel and a shore station. The other options are incorrect: * **Ch-70** is a Marine VHF channel used for Digital Selective Calling (DSC), a digital calling system, not for voice duplex communications. It operates in simplex mode for digital signals. * **Ch-5A** and **Ch-22A** are Marine VHF channels designated for **simplex** operation. The "A" suffix often indicates a simplex channel in the US, typically used for ship-to-ship or non-public coast station communications, where stations transmit and receive on the same frequency (or a single frequency for one-way broadcasts, like Ch-22A used by the Coast Guard).