The correct answer is C. Nadir.
The nadir is the point on the celestial sphere vertically below the observer’s position. It is the opposite of the zenith, which is the point on the celestial sphere directly above the observer’s position.
The celestial sphere is an imaginary sphere that surrounds the Earth. It is used to represent the sky and the positions of the stars. The nadir is located on the celestial sphere directly below the observer’s horizon.
The nadir is an important point in astronomy and astrology. It is used to calculate the positions of the stars and planets. It is also used to determine the time of day.
The nadir is also an important point in mythology and religion. It is often associated with the underworld and the dead.