The ocean bottom that extends from the shoreline out to an area where there is a marked change in slope to a greater depth is the（）.

A.of the wave's crest
B.of the wave's trough
C.measured from crest to trough
D.measured from crest to crest

A.at right angles to the flow of the current
B.against the flow of the current
C.in the same direction as the flow of the current
D.over slack water

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