Explanation: The auto alarm receiver is critically important for maritime safety, designed to detect the international distress signal. Historically, 500 kHz was the primary international Morse code distress frequency. For reliable detection, especially considering potential frequency drift or minor inaccuracies in transmitting stations, international regulations specify that the receiver must be tuned to 500 kHz but also capable of responding to signals within a defined bandwidth around this central frequency. This required bandwidth is 500 kHz +/- 12.5 kHz. Therefore, the receiver must respond to signals from 487.5 kHz (500 kHz - 12.5 kHz) to 512.5 kHz (500 kHz + 12.5 kHz). Option A correctly identifies this precise regulatory requirement. The other options provide incorrect bandwidth ranges for this critical safety system.