单项选择题
The captain wants to see the （）.
A. chief officer B. second officer C. third officer D. carpenter
单项选择题 Echo sounder sends a（） (无线电信号)from the bottom of the ship to the seabed.
单项选择题 Radar is of great help to ship in poor（）(能见度).
单项选择题 Navigators use navigational aids, such as（）（罗经）.
