The correct answer is: A. Astronomical latitude
Astronomical latitude is the angle between the vertical at the station of observation and the equatorial plane. It is measured in degrees north or south of the equator.
Astronomical co-latitude is the angle between the vertical at the station of observation and the polar axis. It is equal to 90 degrees minus the astronomical latitude.
Co-declination of a star is the angle between the star’s declination and the celestial equator. It is measured in degrees north or south of the equator.
Declination of a star is the angle between the star’s position and the celestial equator. It is measured in degrees north or south of the equator.
The astronomical latitude is the most important of these four angles because it is used to calculate the position of stars in the sky. The other three angles are used to calculate the position of the sun and moon in the sky.