单项选择题
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
单项选择题 The edge of a hurricane has overtaken your vessel in the Gulf of Mexico，and the northwest wind of a few hours ago has shifted to the west. This is an indication that you are located in the（）.
单项选择题 The drift and set of tidal，river，and ocean currents refer to the（）.
单项选择题 The direction of the surface wind is（）.