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（）.
A.21-Aug-99 B.21-Sep-99 C.Octoer 31，1999 D.31-Dec-99
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（）.
单项选择题 Deviation in a compass is caused by the（）.
