单项选择题
A.They are not subject to permanent magnetism; no check is necessary B.Semiannually C.Annually D.Every five years
The Flinders bar on a magnetic compass compensates for ...
单项选择题The Flinders bar on a magnetic compass compensates for the（）.
A.Induced magnetism in vertical soft iron B.Induced magnetism in horizontal soft iron C.Permanent magnetism in ship's steel D.Vessel's inclination from the vertical
In more recent years，（）has been used by civilians in ma...
单项选择题In more recent years，（）has been used by civilians in many new ways to determine positions，such as in automobile and boat navigation，hiking，emergency rescue，and precision agriculture and mining.
A.GPS B.GMDSS C.AIS D.Navtex
By convention，the north seeking ends of a compass’ magn...
单项选择题By convention，the north seeking ends of a compass’ magnets are colored（）.
A.Black B.Blue C.Red D.White
