单项选择题
The meaning of ebb tide is that （）.
A.tide is falling from high water to low water B.tide is rising from low water to high water C.tide is reaching to a highest level D.tide is reaching to a lowest level
单项选择题 The height of tide is the （）.
单项选择题 The height of eye correction is smaller than geometrical dip because of （）.
单项选择题 The height of a light is measured from which reference plane?（）
