A.variation
B.deviation
C.variation and deviation
D.a correction for the direction of current set

A.use the magnets one at a time，putting one in one side and then one on the opposite side，one step higher
B.use the magnets in pairs，starting at the top，with trays at the highest point of travel
C.use the magnets in pairs，from the bottom up，with the trays at the lowest point of travel
D.fill all the trays with magnets，then remove them one-by-one until the deviation is removed

A.before correcting for any deviation
B.after correcting for variation
C.after adjusting the fore-and-aft and athwartships permanent magnets
D.before the quadrantal correctors are placed on the compass

A.The course change should be made rapidly to prevent transient induced magnetism while passing the intercardinal headings
B.After the new heading is reached，the vessel should steam on that course for at least two minutes before the adjustment
C.During the course change，you should gently tap the compass to remove any error caused by friction on the pivot bearing
D.After steadying on the new heading，the compass card should be slewed by a magnet and allowed to oscillate freely to remove any gaussin error

A.be shielded from direct sunlight
B.be locked into a constant heading
C.have any air bubbles replaced with nitrogen
D.have the compensating magnets removed