单项选择题
Which magnetic compass corrector（s）CANNOT be set on a heading of magnetic east or magnetic west（）.
A.Heeling magnet B.Flinders bar C.Fore-and-aft magnets D.All of the above can be set on magnetic east or magnetic west headings
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（）.
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（）.
