单项选择题
A.only one high and one low water occur during a lunar day
B.the high tide is higher and the low tide is lower than usual
C.the high tide and low tide are exactly six hours apart
D.two high tides occur during a lunar day
单项选择题 Your vessel is docking, but not yet alongside. Which line will be the most useful when maneuvering the vessel alongside the pier?（）.
单项选择题 What is a CORRECT reply to a pilot’s request, How’s your heading?（）
单项选择题 Shipboard Emergency Drills must be carried out at least（）on board cargo ship.