单项选择题
Spring tides are tides that（）.
A.have lows lower than normal and highs higher than normal B.have lows higher than normal and highs lower than normal C.are unpredictable D.occur in the spring of the year
单项选择题 Set of current is（）.
单项选择题 Scouring is the result of（）.
单项选择题 River currents tend to（）.
