单项选择题
A.deviation minus variation
B.variation plus compass course
C.combined variation and deviation
D.difference between true and magnetic heading
单项选择题 Compass deviation is caused by（）.
单项选择题 Before a magnetic compass is adjusted certain correctors must be checked to ensure that they are free of permanent magnetism. These correctors are the（）.
单项选择题 Based on your 2209 fix，which would be a warning that you are being set down on Block Island Sound South Entrance Obstruction Lighted BIS Buoy? （）