单项选择题
Which magnetic compass corrector（s）can be set while the vessel is on a heading of magnetic north or magnetic south（）.
A.Quadrantal spheres B.Heeling magnets C.Flinders bar D.Fore-and-aft magnets
单项选择题 Which compensates for errors introduced when the vessel heels over（）.
单项选择题 When relieving the helm，the new helmsman should know the（）.
单项选择题 When crossing the magnetic equator the（）.
