单项选择题
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
单项选择题 The height of a wave is the vertical distance（）.
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（）.