单项选择题
A.slip B.sidewise force C.rotational force D.thrust
The fog is lifted，so（）the radar．A.closeB.openC.switch o...
单项选择题The fog is lifted，so（）the radar．
A.close B.open C.switch off D.switch on
The external flotation bladder of an immersion suit sho...
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
The dumping of refuse in a lock is permitted（）.A.when a...
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
