A.An agonic lineB.The magnetic equatorC.A magnetic meri……

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

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

单项选择题Any piece of metal on becoming magnetized will develop regions of concentrated magnetism called（）.

A.flux
B.poles
C.magnets
D.azimuth