Explanation: An EPIRB's (Emergency Position-Indicating Radio Beacon) strobe light is specifically designed for *visual* detection of a distressed vessel, especially during low-light conditions or at night. It emits a bright, flashing light that can be seen by search aircraft or vessels. The other options involve radio frequency transmissions: A) A 9-GHz SART (Search And Rescue Transponder) beacon transmits a signal that creates a series of dots on a search radar display, an electronic, not visual, detection method. C) A 121.5-MHz EPIRB beacon and D) A 406-MHz EPIRB beacon transmit radio signals. The 406 MHz signal alerts satellites with position data, and the 121.5 MHz signal is used for local homing. Neither of these radio signals is directly visible to the human eye.