单项选择题
Current refers to the（）.
A.vertical movement of the water B.horizontal movement of the water C.density changes in the water D.None of the above
单项选择题 A structure，usually made of stone，or cement pilings，which extends from the bank at approximately right angles to the current is called a（）.
单项选择题 A stream of water immediately surrounding a moving vessel’s hull，flowing in the same direction as the vessel is known as（）.
