Explanation: Search and Rescue Transponders (SARTs) operate in the 9 GHz frequency band, which corresponds to the X-band radar frequency range (typically 9.2-9.5 GHz). This specific band is chosen because SARTs are designed to be detected by standard marine X-band radar systems carried on vessels. When a SART is interrogated by an X-band radar signal, it responds by transmitting a series of 12 distinctive pulses sweeping across the 9 GHz band. This creates a unique line of dots on the interrogating vessel's radar display, indicating the SART's location and direction. Other options are incorrect: 3 GHz (S-band) is another common marine radar band, but SARTs are not designed to operate there. 406 MHz is the distress frequency used by Emergency Position-Indicating Radiobeacons (EPIRBs) and Personal Locator Beacons (PLBs) for satellite alerting, not for direct shipboard radar detection.