Explanation: Search and Rescue Transponders (SARTs) are designed to be detected by standard marine radar systems. These radars primarily operate in the X-band, which covers frequencies from approximately 8 to 12 GHz. When a SART detects a radar pulse from an X-band radar, it responds by transmitting a series of pulses back on the same frequency band. This response creates a distinctive line of dots on the radar display, indicating the SART's location. Therefore, 9 GHz falls directly within the operational X-band for SARTs. Options A and B (3 GHz and S-band) are much lower frequencies, typically used for other radar types or communication, but not for SARTs. Option C (406 MHz) is the distress frequency used by Emergency Position-Indicating Radiobeacons (EPIRBs) and Personal Locator Beacons (PLBs) to transmit signals to satellites, not for radar-based SART detection.