Explanation: A SART, or Search and Rescue Transponder, functions as a radar transponder. When placed in the "on" position, it enters a listening state, ready to detect signals. It does not transmit continuously or immediately upon activation. Instead, a SART is specifically designed to respond to a marine radar signal. Upon detecting the unique sweep of a 9-GHz X-band radar from a searching vessel or aircraft, the SART will begin transmitting a series of 12 dots on the radar screen, showing rescuers its precise location. Therefore, option C correctly describes this behavior: it responds *after* being interrogated by a 9-GHz RADAR signal. Options A and D are incorrect because SARTs do not transmit continuously or immediately upon water detection (which is more characteristic of some EPIRBs or PLBs for initial activation, but not a SART's transmission trigger). Option B is partially true as it must be manually activated to be ready, but it doesn't describe *when* it begins transmitting.