單項(xiàng)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(xiàng)選擇題The apparent wind’s speed can be zero only when two conditions are present. One condition is that the true wind（）.

A.must be from dead ahead
B.speed must be zero
C.must be from dead astern
D.must be on the beam

2.單項(xiàng)選擇題Ocean currents are well defined and（）.

A.create large waves in the direction of the current
B.change direction 360°during a 24 hour period
C.remain fairly constant in direction and velocity throughout the year
D.are characterized by a light green color

5.單項(xiàng)選擇題Advection fog is most commonly caused by（）.

A.air being warmed above the dew point
B.saturation of cold air by rain
C.a rapid cooling of the air near the surface of the Earth at night
D.warm moist air being blown over a colder surface

6.單項(xiàng)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

7.單項(xiàng)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(xiàng)選擇題The horse latitudes are characterized by（）.

A.weak pressure gradients and light，variable winds
B.the formation of typhoons or hurricanes in certain seasons
C.steady winds in one direction for six months followed by wind reversal for the next six months
D.steady winds generally from the southeast in the Southern Hemisphere

9.單項(xiàng)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