A.only after two hours in the waterB.only after four ho……

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（）.

A.it increases the likelihood of collision between the towing vessel and the disabled vessel
B.recreational boaters tend to make the heaving line fast to the towed vessel as if it were the towline
C.the monkey fist may injure someone
D.it may reduce the catenary and increase yawing

单项选择题The direction in which a vessel is steered is the course. The path actually followed is the （）.

A.route
B.track
C.heading
D.course over the ground

单项选择题The direction a vessel is pointed at any given time is the（）.

A.course
B.track
C.heading
D.course over the ground

单项选择题The difference in water spray pattern between the high-velocity tip and low-velocity applicator used with the all-purpose nozzle is due to（）.

A.a difference in water pressure
B.the method of breaking up the water stream
C.the length of the applicator
D.All of the above