单项选择题

The line which connects the points of zero magnetic dip is（）.

A.An agonic line
B.The magnetic equator
C.A magnetic meridian
D.All of the above

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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

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