Explanation: When a vessel's USA-INT switch is set to INT, its radio configures the selected channel according to international frequency assignments. The Coast Guard, operating in U.S. waters, expects communications on channels configured for U.S. standards. Channel 22 (often 22A for Coast Guard liaison) is a duplex channel in the U.S., meaning the vessel transmits on one frequency and receives on a different frequency. The Coast Guard transmits and receives on corresponding paired frequencies. However, if the radio is set to INT, it might configure Ch-22 as a simplex channel or use different duplex frequencies that don't match the U.S. standard. In this specific scenario, the vessel transmitting on Ch-22 in INT mode will likely transmit on a frequency that the Coast Guard, listening on their U.S. standard receive frequency for Ch-22, can hear. However, when the Coast Guard responds on their U.S. standard transmit frequency for Ch-22 (which is different from their receive frequency), the vessel, operating in INT mode (possibly simplex or a different duplex pair), will be listening on the wrong frequency and will not hear the Coast Guard's reply. Therefore, the Coast Guard hears the initial call, but the vessel cannot hear the response.