The force exerted by a propeller which tends to throw the stern right or left is called（）.

单项选择题The fog is lifted，so（）the radar．

A.close
B.open
C.switch off
D.switch on

单项选择题The external flotation bladder of an immersion suit should be inflated（）.

A.only after two hours in the water
B.only after four hours in the water
C.before entry into the water
D.upon entry into the water

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