Explanation: VHF marine radios are designed with different channel plans to accommodate regional regulations. The "USA" setting configures the radio for the specific channel assignments and operational modes mandated for U.S. waters. **B) Using the “USA” setting changes certain channels from duplex to simplex operation.** This statement is true. For example, internationally (under the "INT" setting), Channel 13 is often a duplex channel used for port operations, and Channel 22 is a duplex channel for public correspondence. However, in the U.S. ("USA" setting), Channel 13 becomes a simplex channel for Bridge-to-Bridge communications, and Channel 22A (an offshoot of 22) is used as a simplex working channel, often by the Coast Guard. Thus, the "USA" setting indeed reconfigures these channels from a potential duplex operation (as per international standards) to simplex operation for specific U.S. uses. **A) You should always use the “INT” setting for calling a Public Correspondence station.** This is incorrect. While "INT" refers to the international plan, the proper channels for public correspondence (if available) depend on the specific region. In U.S. waters, you would use the "USA" setting. Ch-16 is the primary calling channel regardless. **C) You should use Ch-22 when calling the U. S. Coast Guard.** This is incorrect. The primary calling channel for the U.S. Coast Guard (and all other vessels for distress, urgency, or safety) is Channel 16. Ch-22A is often used by the Coast Guard as a working channel after initial contact on Ch-16. **D) Using the “INT” setting will prevent proper Ch-13 Bridge-to-Bridge operations.** While factually true (because Ch-13 is simplex in USA mode and duplex with a different transmit frequency in INT mode, causing a communication mismatch), statement B is a more fundamental and general description of how the "USA" setting reconfigures the channel plan, including the operational mode of certain channels. B describes what the setting *does*, while D describes a consequence of using the *wrong* setting.