单项选择题
Which compensates for errors introduced when the vessel heels over（）.
A.The soft iron spheres on the arms of the binnacle B.Magnets placed in trays inside the binnacle C.A single vertical magnet beneath the compass D.The Flinders bar
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（）.
单项选择题 What is used to correct for both induced and permanent magnetism，and consequently must be readjusted with radical changes in latitude（）.
