單項(xiàng)選擇題Which of the following statements is TRUE regarding automatic identification systems（AIS）（）.

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


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3.單項(xiàng)選擇題What does not contribute to the commercial GPS receiver position error（）.

A.Satellite clock
B.Ship's speed
C.Atmospheric/ionospheric propagation
D.Receiver

4.單項(xiàng)選擇題To obtain accuracy in fixing by DF，（）and three stations should be used.

A.Parallel bearings
B.Long-range bearings
C.Short-range bearings
D.Cross bearings

5.單項(xiàng)選擇題The use of pulse groups and extremely precise timing at each Loran-C station makes possible the use of（）.

A.High frequency pulses
B.Combinations of high and low frequency pulses
C.The same frequency for all stations in a chain
D.Varied long and short pulses