单项选择题
The dumping of refuse in a lock is permitted（）.
A.when approved by the lockmaster B.when locking downbound C.at no time D.during high water only
单项选择题 The disadvantage of using a heaving line to pass a towline is that（）.
单项选择题 The direction in which a vessel is steered is the course. The path actually followed is the （）.
单项选择题 The direction a vessel is pointed at any given time is the（）.
