（）is used for calling and replying,and for transmitting acknowleding and relaying distress alerts.

单项选择题（）provides a paper trace of course steered by the vessel against time.

A.The echo sounder
B.The radar
C.The course recorder
D.The direction finder

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

A.The echo sounder
B.The radar
C.The course recorder
D.The direction finder

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