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

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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

单项选择题

On a chart，the characteristic of the light on a lighthouse is shown as flashing white with a red sector.The red sector（）.

A.Indicates the limits of the navigable channel
B.Indicates a danger area
C.Is used to identify the characteristics of the light
D.Serves no significant purpose

单项选择题

In very high latitudes，the most practical chart projection is the（）.

A.Mercator
B.Gnomonic
C.Azimuthal
D.Lambert conformal