单项选择题
A snag or other underwater obstruction may form a（）.
A.V-shaped ripple with the point of the V pointing upstream
B.V-shaped ripple with the point of the V pointing downstream
C.small patch of smooth water on a windy day
D.smoothing out of the vessel's wake
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相关考题
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单项选择题
A section of the river that is narrower than usual and is often navigable from bank to bank is a（）.
A.chute
B.stabilized channel
C.slough
D.navigable pass -
单项选择题
A rotary current sets through all directions of the compass. The time it takes to complete one of these cycles is approximately（）.
A.3 hours
B.6 1/2 hours
C.12 1/2 hours
D.25 hours -
单项选择题
A light，feathery deposit of ice caused by the sublimation of water vapor directly into the crystalline form，on objects whose temperatures are below freezing，is called（）.
A.dew
B.frost
C.glaze
D.snow
