单项选择题
Error may be introduced into a magnetic compass by（）.
A.making a structural change to the vessel B.a short circuit near the compass C.belt buckles D.All of the above
单项选择题 Gyrocompass repeaters reproduce the indications of the master gyrocompass. They are（）.
单项选择题 How is variation indicated on a small-scale nautical chart?（）.
单项选择题 If（）is shut down for an extended time optimum position fixing will take up to 2 hours after power is reapplied．
