单项选择题
The Flinders bar and the quadrantal spheres should be tested for permanent magnetism at what interval（）.
A.They are not subject to permanent magnetism; no check is necessary
B.Semiannually
C.Annually
D.Every five years
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相关考题
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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 -
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 -
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
