单项选择题
Mean high water is the average height of（）.
A.The higher high waters B.The lower high waters C.The lower of the two daily tides D.All high waters
单项选择题 Mariners not entering the port are（）to keep at least one mile off.
单项选择题 Many of the lights on this coast are placed so high as to be frequently obscured by（）.
单项选择题 Lines drawn through points on the Earth having the same atmospheric pressure are known as （）.
