单项选择题
Variation is the angular measurement between（）.
A.compass north and magnetic north B.compass north and true north C.magnetic meridian and the geographic meridian D.your vessel's heading and the magnetic meridian
单项选择题 Variation is a compass error that you（）.
单项选择题 Variation in a compass is caused by（）.
单项选择题 True heading differs from magnetic heading by（）.
