单项选择题
Magnets in the binnacles of magnetic compasses are used to reduce the effect of（）.
A.deviation B.variation C.local attraction D.All of the above
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.
单项选择题 Induced magnetism is found in（）.
