单项选择题
The greatest directive force is exerted on the magnetic compass when the（）.
A.needles are nearly in line with the meridian B.vessel is near the magnetic poles C.variation is near zero D.vessel is near the magnetic equator
单项选择题 The Flinders bar on a magnetic compass compensates for the（）.
单项选择题 The error in a magnetic compass caused by the vessel’s magnetism is called（）.
单项选择题 The directive force of a gyrocompass（）.
