the forebearing of AB and back bearing of AB differ by 180°

the forebearing of AB and back bearing of BA differ by 180°

both (a) and (b) are correct.

none is correct

incorrect levelling of the magnetic needle

loss of magnetism of the needle

friction of the needle at the pivot

presence of magnetic substances near the instrument

W23° 30'N

N66° 30'W

S113° 30'N

N23° 30'W

give whole circle bearing (WCB) of a line and quadrantal bearing (QB) of a line respectively

both give QB of a line and WCB of a line

both give QB of a line

both give WCB of a line

azimuth

declination

local attraction

magnetic bearing