单项选择题
When there are small differences between the heights of two successive high tides or two successive low tides，the tides are called（）.
A.Diurna B.Semi-diurnal C.Solar D.Mixed
单项选择题 When daylight savings time is kept，the time of tide and current calculations must be adjusted.One way of doing this is to（）.
单项选择题 Tides are superimposed on nontidal rising and falling water levels，caused by（）．
单项选择题 The set of the current is the（）.
