单项选择题
Magnets are placed in horizontal trays in the compass binnacle to compensate for the（）.
A.induced magnetism in the vessel's horizontal soft iron B.change in the magnetic field when the vessel inclines from vertical C.permanent magnetism of the vessel D.magnetic fields caused by electrical currents in the vicinity
单项选择题 Magnetic variation changes with a change in（）.
单项选择题 Magnetic heading differs from compass heading by（）.
单项选择题 Magnetic dip is a measurement of the angle between the（）.
