（）is a radio receiver with ablity to sense direction of the incoming radio waves.

单项选择题（）is an equipment used to detect the presence of ships ,buoys,coast and many other targels and to obtain range and bearing of these targets.

A.The marine sextant
B.The chronometer
C.The echo sounder
D.The radar

单项选择题（）sends a radio signal from the bottom of the ship to the sea-bed,from which it is reflected.

A.The marine sextant
B.The chronometer
C.The echo sounder
D.The radar

单项选择题（）is the navigational timekeeper of the vessel.

A.The marine sextant
B.The chronometer
C.The magnetic compass
D.The gyrocompass

单项选择题（）is used for measuring horizontal and vertical angles.

A.The marine sextant
B.Thechronometer
C.The magnetic compass
D.The gyrocompass

单项选择题（）means rudder to be held in the force and aft angles.

A.Steady
B.Meet her
C.Midships
D.Stop engines