单项选择题
A.Magnetic compass table
B.Magnetic meridians
C.Isogonic lines
D.Variation is not indicated on small-scale nautical charts
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．
单项选择题 If a magnetic compass is not affected by any magnetic field other than the Earth’s，which statement is TRUE?（）.
单项选择题 If the compass heading and the magnetic heading are the same then（）.