A.DSC provides reception of weather and navigational warnings plus search and rescue information
B.DSC provides low-cost，routine communications for the vessel operator
C.DSC is to be used for transmitting and receiving distress alerts to and from other ships or coast radio stations via radio
D.This aids SAR authorities in tracking a vessel's position by satellite

A.SART
B.EPIRB
C.NAVTEX
D.INMARSAT-B