单项选择题
The best time to work a boat into a slip is（）.
A.when the wind is against you B.with the current setting against you C.at slack water D.with a cross current
单项选择题 The Benguela Current flows in a（）.
单项选择题 Swell is the rise and fall of the ocean’s surface due to（）.
单项选择题 Stand of the tide is that time when（）.
