单项选择题

The characteristic of a lighted cardinal mark may be （）.

A.very quick flashing
B.flashing
C.fixed
D.occulting

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单项选择题

A.pressure changes in the air mass
B.movement of the air mass
C.the heterogeneous nature of the air mass
D.upper level atmospheric changes

单项选择题

A.which
B.where
C.what
D.who

单项选择题

A.specified by international authorities
B.specified by national authorities
C.on standard map
D.on the chart or Sailing Directions in use