无线DDN业务应用范围有哪些？

（）is the distance east or west measured in degrees，minutes and seconds of arc on the equator between the prime meridian and the meridian passing through the place.

A. Longitude
B. Latitude
C. Height
D. Bearing

A gnomonic projection is based on a(n)（）.

A. plane tangent at one point
B. cylinder tangent at the equator
C. cone tangent at one parallel
D. infinite series of cones tangent at selected parallel

A light having characteristics which include color variations is defined as（）.

A. switching
B. alternating
C. oscillating
D. fluctuating

A lighthouse can be identified by its（）.

A. painted color
B. light color and phase characteristic
C. type of structure
D. All of the above

A line of position formed by sighting two charted objects in line is called a(n)（）.

A. relative bearing
B. range line
C. track line
D. estimated positio