单项选择题
In the horizon system of coordinates what is equivalent to the equator on the Earth?（）.
A.Prime vertical circle B.Principal vertical circle C.Parallels of altitude D.Horizon
单项选择题 In order for a star to be used for a sight at lower transit，the star must（）.
单项选择题 In low latitudes，a first quarter Moon will always rise at about（）.
单项选择题 In general，the most effective period for observing stars and planets occurs during the darker limit of（）.
