Explanation: The USA-INT control, found on some amateur radio transceivers, particularly those with channelized modes or multi-band capabilities (e.g., HF/VHF), manages pre-configured frequency operations. Certain channels, often those designated for international calling frequencies, satellite operations, or specific repeater systems, may be pre-programmed to operate in duplex mode (transmitting on one frequency and receiving on another). The "USA-INT" function allows the operator to override this default or programmed duplex configuration. When activated, it enables these typically duplex channels to be used in simplex mode, where both transmission and reception occur on the same frequency. This provides flexibility by allowing a channel normally set for duplex operation to function as a simplex channel. Option A is incorrect because this control typically facilitates the reverse: changing duplex to simplex. Option C is incorrect; the control has no direct bearing on increasing radio range, which depends on power, antenna, and propagation. Therefore, option B accurately describes its purpose.