Explanation: COSPAS-SARSAT is an international satellite-based search and rescue system, operating exclusively for distress alerting. Statement C is false because COSPAS-SARSAT satellites are dedicated solely to receiving and relaying distress signals from EPIRBs, ELTs, and PLBs. They are not used for commercial messaging or general communication traffic. Commercial messages would use dedicated telecommunication satellite systems. Statements A, B, and D are true: * A) EPIRBs, ELTs, and PLBs are distress beacons, and COSPAS-SARSAT is the primary system for receiving their distress alerts. * B) The system's primary frequency for monitoring distress beacons is 406 MHz. * D) COSPAS-SARSAT satellites utilize the Doppler shift in the 406 MHz signal to calculate the beacon's location, especially for beacons not equipped with integrated GPS.