单项选择题
A star is observed at lower transit. The line of position derived from this sight is（）.
A.on the prime vertical B.a latitude line C.a longitude line D.of no special significance
单项选择题 A sidereal day is shorter than a solar day. This difference is due to（）.
单项选择题 A sidereal day is approximately how much shorter than a solar day?（）
单项选择题 A sextant having an index error that is off the arc has a（）.
