单项选择题
A.parallax and personal error B.inaccuracies in the reading and reference level C.visibility and magnitude D.All of the above are correct
A.is most accurate before sunrise B.is most accurate after sunset C.should only be observed when the Sun's lower limb is above the horizon D.is most accurate when the Sun's center is observed on the visible horizon
A.Hercules B.Cygnus C.Aquila D.Capricorn