Explanation: The USA-INT control on VHF marine radios allows the operator to switch between U.S. and International channel assignments. Many channels that are designated for duplex operation internationally are assigned for simplex operation in the U.S. for non-commercial vessel communication, particularly in coastal waters. **C) Correctly set, will result in simplex operations in U.S. Coastal waters on the "alpha" channels.** This is correct. When the radio is set to "USA," it configures these channels (e.g., 68A, 69A, 71A) for simplex operation as required by U.S. regulations for recreational vessels. This ensures local, direct vessel-to-vessel communication without relying on repeaters, even though the equivalent international channels might be duplex. **A) Was made necessary by a desire for more duplex channels in the U.S.** Incorrect. The control often converts international duplex channels to U.S. simplex channels, reducing the number of duplex channels available for general use, not increasing them. **B) Correctly set, will result in duplex operations in U.S. Coastal waters on the "alpha" channels.** Incorrect. The "alpha" channels (e.g., 68A, 69A, 71A) are specifically designated for simplex operation in U.S. coastal waters when the radio is set to "USA." **D) Was made necessary by a desire to convert simplex international channels to duplex channels in the U.S.** Incorrect. It is the opposite; it converts *duplex* international channels to *simplex* in the U.S. to comply with domestic regulations.