单项选择题
Radar is of great help to ship in poor（）(能见度).
A.visibility B.VHF C.visible D.compass
单项选择题 Navigators use navigational aids, such as（）（罗经）.
单项选择题 （）（电罗经）can tell us true north.
单项选择题 Officers observe ships with a pair of （）（望远镜）.
