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.
A.hammering and jarring B.vibration and pounding C.varying magnetic fields D.stable or permanent magnetism of the ship
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（）.
单项选择题 When adjusting a magnetic compass for error，a deviation table should be made（）.
