单项选择题

The points on the earth’s surface where the magnetic dip is 90° are（）.

A.Along the magnetic equator
B.Connected by the isoclinal line
C.The isopors
D.The magnetic poles

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单项选择题

The four standard light colors used for lighted aids to navigation are red，green，white，and （）.

A.purple
B.orange
C.blue
D.yellow

单项选择题

The equator is（）.

A.the primary great circle of the Earth perpendicular to the axis
B.the line to which all celestial observations are reduced
C.the line from which a celestial body's altitude is measured
D.All of the above

单项选择题

Restricted areas at locks and dams are indicated by（）.

A.Flashing red lights upstream and fixed red lights downstream
B.Yellow unlighted buoys
C.Signs and/or flashing red lights
D.Red daymarks upstream and green daymarks downstream