The brightness of a star is most dependent on the star' why. a. mass b. density c. shape d. temperature

I would say the answer is A - a stars mass

The majority of stars in the galaxy, including our Sun, Sirius and Alpha Centauri A and B are all main sequence stars.

Mass is the key factor in determining the lifespan of a main sequence star, its size and its luminosity ( brightness)

Two characteristics define brightness: luminosity and magnitude. Luminosity is the amount of light that a star radiates. The size of the star and its surface temperature determine its luminosity. Apparent magnitude of a star is its perceived brightness, factoring in size and distance, while absolute magnitude is its true brightness irrespective of its distance from earth.

Its the second one nonmetals are moldable and easily shaped