单项选择题
Most GPS receivers use the doppler shift of the carrier phase to compute（）.
A.Latitude B.Longitude C.Speed D.Time
单项选择题 Magnets in the binnacles of magnetic compasses are used to reduce the effect of（）.
单项选择题 It may be found that，in certain circumstances，Radar Beacon can cause unwanted interference particularly（）.
单项选择题 It is dangerous for vessels without the use of radar（）the estuary.
