Answer is: B. apparent magnitude.
The magnitude of star is a measure of its brightness. The lower the magnitude number, the brighter the star.
Apparent magnitude is the brightness of a star as seen from Earth.
Absolute magnitude is the apparent magnitude of a star (or some other astronomical object) if it were 32.6 light years away from Earth and in the absence of any sources (dust, gases) that could interfere with its brightness.
Luminosity is the total amount of energy emitted per unit of time by a star.
