单项选择题
A.6.27 B.8.36 C.10.45 D.18.81
A.在赤道附近最短 B.在纬度45°附近最短 C.在两极附近最短 D.固定不变
A.1842.9m B.1852.3m C.1852.0m D.1861.6m