单项选择题
A.The echo sounder B.The radar C.The course recorder D.The direction finder
（）is an equipment used to detect the presence of ships ...
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
（）sends a radio signal from the bottom of the ship to t...
单项选择题（）sends a radio signal from the bottom of the ship to the sea-bed,from which it is reflected.
（）is the navigational timekeeper of the vessel.A.The ma...
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
