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 Due to GPS roll over of the clock cycle，GPS receivers may give the wrong time and position or may lock up permanently on（）.
单项选择题 Deviation which is maximum on intercardinal compass headings may be removed by the（）.
单项选择题 Deviation is the angle between the（）.
