Explanation: A Search and Rescue Transponder (SART) is a type of radar beacon used to pinpoint the location of a distress incident or survival craft. After being manually or water activated, the SART does not continuously radiate. Instead, it operates as a transponder. It listens for pulses from X-band marine RADARs operating in the 9 GHz band. Upon receiving a RADAR interrogation pulse, the SART immediately transmits a series of 12 distinct sweep signals back to the RADAR. These signals appear as a line of dots on the RADAR display, indicating the SART's position and helping search and rescue vessels navigate towards it. Therefore, the SART only begins to transmit *in response* to an incoming RADAR signal, making option B correct. Options A and C are incorrect because they imply continuous radiation after activation, which is not how a SART works. Option D is incorrect as SARTs are automatic responders, not manually keyed devices.