单项选择题
A.If the blue ends of the magnets are aft，and the fore-and-aft tray is at the top，you should add some magnets
B.If the blue ends of the magnets are aft you should lower the fore-and-aft tray
C.If the blue ends of the magnets are aft，and the fore-and-aft tray is at the top，you should reverse the magnets
D.If the blue ends of the magnets are forward，and the fore-and-aft tray is at the bottom，you should add some magnets
单项选择题 A ship under construction or major repair will acquire permanent magnetism due to（）while sitting stationary in the earth’s magnetic field.
单项选择题 When changing from a compass course to a true course you should apply（）.
单项选择题 When adjusting a magnetic compass using the fore-and-aft permanent magnets，you should（）.