When visibility is 20 nautical miles, we say that visibility is（）.

单项选择题Our ship has not been to shipyard for a long time, the fouling on the ship’s hull greatly decreases her（）.

A.resistance
B.weight
C.speed
D.displacement

单项选择题Radar is not only to obtain（）,but also to measure their distance away from you.

A.brightness of obtain
B.color of targets
C.shape of targets
D.bearing of objects

单项选择题The anchor was then（）and the siren sounded.

A.aweigh
B.weight
C.weigh
D.weighing

单项选择题Are there many（）and warehouses in the port?

A.wharf
B.wharves
C.wharve
D.wharfs

单项选择题The quartermasters（）steer the ship and help the officer keep lookout.

A.duty
B.on duty
C.at duty
D.in duty