单项选择题
A sidereal day is approximately how much shorter than a solar day?（）
A.4 minutes B.8 minutes C.12 minutes D.16 minutes
单项选择题 A sextant having an index error that is off the arc has a（）.
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（）.
