A.AIS is a global tracking system that relies upon INMARSAT C service to communicate vessel position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area
B.AIS is a short-range 3 cm X-band radar system that automatically sends a vessel's position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area
C.AIS is a short-range VHF-FM system that automatically broadcasts a vessel's position and other safety related information frequently to similarly equipped vessels，aircraft and shore stations within the area
D.AIS is a one-way centrally managed system that requires the local VTS to send commands to instruct each vessel to broadcast position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area

A.Radar
B.GPS
C.DF
D.Satellite Navigator