單項(xiàng)選擇題The velocity of the current in large coastal harbors is（）.

A.predicted in Tidal Current Tables
B.unpredictable
C.generally constant
D.generally too weak to be of concern


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1.單項(xiàng)選擇題The velocity of a rotary tidal current will be decreased when the Moon is（）.

A.at apogee
B.new
C.full
D.All of the above

2.單項(xiàng)選擇題The type of current which will have the greatest effect on the course made good for your vessel is（）.

A.one flowing in the same direction as your course steered
B.one flowing in the opposite direction as your course steered
C.one that flows at nearly right angles to your course steered
D.a rotary current in which the direction of current flow constantly changes

3.單項(xiàng)選擇題The two most effective generating forces of surface ocean currents are（）.

A.temperature and salinity differences in the water
B.wind and density differences in the water
C.water depth and underwater topography
D.rotation of the Earth and continental interference

4.單項(xiàng)選擇題The tide is（）.

A.black
B.setting
C.being
D.having

5.單項(xiàng)選擇題The tide（）.It’s 2 hours before low water，and（）your present position you will be aground at low water.

A.falls／in
B.has been falling／on
C.has fallen／at
D.is falling／in