单项选择题
A sextant having an index error that is off the arc has a（）.
A.positive correction B.dip error C.negative correction D.semidiameter error
单项选择题 A semidiameter correction is applied to observations of（）.
单项选择题 A phase correction may be applicable to correct the sextant altitude correction of（）.
单项选择题 A phase correction is applied to observations of（）.
