單項選擇題A backlash below a lock is defined as（）.

A.a current setting your vessel on the wall
B.a current setting into the lock chamber
C.an eddy working along the lower guide wall
D.a current setting counterclockwise


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1.單項選擇題A tide is called diurnal when（）.

A.only one high and one low water occur during a lunar day
B.the high tide is higher and the low tide is lower than usual
C.the high tide and low tide are exactly six hours apart
D.two high tides occur during a lunar day

3.單項選擇題In mid-ocean，the characteristics of a wave are determined by three factors. What is NOT one of these factors?（）.

A.Effect of the moon's gravity
B.Fetch
C.Wind velocity
D.Length of time a wind has been blowing

5.單項選擇題The presence of stratus clouds and a dying wind will usually result in（）.

A.heavy rain
B.heavy snow
C.thick fog
D.clearing skies

6.單項選擇題The height of a wave is the vertical distance（）.

A.from the still water plane to the crest
B.from the still water plane to the trough
C.from crest to trough
D.between water levels at one-quarter of the wave's length

7.單項選擇題The direction of the southeast trade winds is a result of the（）.

A.equatorial current
B.humidity
C.rotation of the earth
D.change of seasons

8.單項選擇題In the Northern Hemisphere the major ocean currents tend to flow（）.

A.clockwise around the North Atlantic and North Pacific Oceans
B.clockwise or counterclockwise depending on whether it is warm or cold current
C.counterclockwise except in the Gulf Stream
D.counterclockwise around the North Atlantic and North Pacific Oceans

10.單項選擇題In a tropical cyclone，in the Northern Hemisphere，a vessel hove to with the wind shifting counterclockwise is（）.

A.ahead of the storm center
B.in the dangerous semicircle
C.in the navigable semicircle
D.directly in the approach path of the storm