Explanation: Search and Rescue Transponders (SARTs) are designed to aid in the location of survival craft by showing a distinctive series of dots on a ship's or aircraft's radar display. They specifically operate in the 9 GHz band, also known as X-band radar frequency (typically 9.2-9.5 GHz). When interrogated by an X-band radar, the SART transmits a sweeping signal that is easily identifiable on the radar screen, directing rescue efforts to the exact location. Options B (3 GHz) and C (S-band) refer to lower radar frequencies, which are not the designated band for SART operation. Option D (406 MHz) is the frequency used by Emergency Position Indicating Radio Beacons (EPIRBs) and Personal Locator Beacons (PLBs) to transmit distress signals via the COSPAS-SARSAT satellite system, a different type of rescue beacon functionality altogether.