A.have lows lower than normal and highs higher than normal
B.have lows higher than normal and highs lower than normal
C.are unpredictable
D.occur in the spring of the year
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A.its velocity in knots
B.direction from which it flows
C.estimated current
D.direction toward which it flows
A.interruption of the normal current flow by the footing
B.elevating in mud-slide zones
C.penetrating rapidly through a hard crust into weaker soils
D.extracting legs from soils with high cohesion
A.pick up speed where the channel widens
B.run slower in the center of the channel
C.hug the inside of a bend
D.cause the greatest depth of water to be along the outside of a bend
A.at times of new and full Moon
B.when the Earth，Moon，and Sun are lying approximately on the same line
C.when the Moon is between first quarter and full and between third quarter and new
D.when the Moon is between new and first quarter and between full and third quarter
A.in an area of high density the water's surface is lower than in an area of low density
B.surface water flows from an area of high density to one of low density
C.the lesser the density gradient the freer the water is to move
D.it is the density differences that cause the currents to stay in the troughs
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Water may boil up around the stern of a vessel in a channel due to（）.
The tide is（）.
Which current is responsible for the movement of icebergs into the North Atlantic shipping lanes（）.
The type of current which will have the greatest effect on the course made good for your vessel is（）.
Neap tides occur when the（）.
To make sure of getting the full advantage of a favorable current，you should reach an entrance or strait at what time in relation to the predicted time of the favorable current?（）
Spring tides are tides that（）.
The velocity of the current in large coastal harbors is（）.
When daylight savings time is kept，the time of tide and current calculations must be adjusted.One way of doing this is to（）.
The term flood current refers to that time when the water（）.