（）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.

（）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.

（）is used for measuring horizontal and vertical angles....

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