what can be found if the apparent magnitude and the distance to a star are known?
a.
velocity
b.
age
c.
absolute magnitude
d.
color

C.  absolute magnitude  

Explanation:

absolute magnitude = apparent magnitude - 5log(distance)  

Thus, if you know the apparent magnitude and the distance, you can calculate the absolute magnitude.

If the apparent magnitude and the distance to a star are known the Absolute magnitude can be found.

Option C

Explanation:

The scale of the relative brightness of the star and other astronomical object that is viewed by the observer is commonly called as Apparent magnitude. The apparent size of the object depends on the internal brightness, distance and decay of light from the object by interstellar dust along the viewer.  

It is a measure of the brightness of the star. Astronomers estimate the size of a star on a scale where the number of bright stars is smaller and the number of dark stars is greater by the Apparent magnitude. In the night sky, Syria is known for the brightest star.