单项选择题
Superior conjunction occurs when（）.
A.the Sun is at maximum declination north or south B.a planet crosses the external plane of the ecliptic C.the Sun is between the Earth and a planet D.two planets are in line
单项选择题 Sidereal time is used by navigators when（）.
单项选择题 Sidereal time is NOT used（）.
单项选择题 Right ascension is primarily used by the navigator for（）.
