单项选择题
The principal purpose of magnetic compass adjustment is to（）.
A.reduce the variation as much as possible B.reduce the deviation as much as possible C.reduce the magnetic dip as much as possible D.allow the compass bowl to swing freely on its gimbals
单项选择题 The permanent magnetism of a vessel may change in strength due to（）.
单项选择题 The permanent magnetism of a vessel may change in polarity due to（）.
单项选择题 The MOST important feature of the material used for making the binnacle of a standard magnetic compass is that it is（）.
