单项选择题
What is the name of the movable，radial guide line used to measure direction on a radar?（）
A.Compass rose B.Cursor C.Plan position indicator D.Variable range marker
单项选择题 What is the basic principle of the magnetic compass?（）
单项选择题 What is an advantage of the magnetic compass aboard vessels?（）
单项选择题 What are the only magnetic compass correctors that correct for both permanent and induced effects of magnetism?（）
