單項選擇題（）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


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1.單項選擇題（）is the navigational timekeeper of the vessel.

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

2.單項選擇題（）is used for measuring horizontal and vertical angles.

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

3.單項選擇題（）means rudder to be held in the force and aft angles.

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

4.單項選擇題（）means check the swing of the vessel’s head in a turn.

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