Which of the following statements is TRUE regarding automatic identification systems (AIS)? （）

AIS is a short-range VHF-FM system that automatically broadcasts a vessel's position，course，speed and other safety related information to all those with similar equipment in the area
B. AIS is a one-way centrally managed system that requires the local VTS to send commands to instruct each vessel to broadcast position，course，speed and other safety related information to all those with similar equipment in the area
C. AIS is a global tracking system that relies upon INMARSAT C service to communicate vessel position，course，speed and other safety related information to all those with similar equipment in the area
D. AIS is a short-range 3 cm X-band radar system that automatically sends a vessel's position，course，speed and other safety related information to all those with similar equipment within the area