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單項(xiàng)選擇題

（）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

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單項(xiàng)選擇題

（）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

單項(xiàng)選擇題

（）is the navigational timekeeper of the vessel.

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