單項選擇題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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2.單項選擇題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

3.單項選擇題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

4.單項選擇題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

5.單項選擇題In very high latitudes，the most practical chart projection is the（）.

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