When an Astronomer Rambles on and on About the Luminosity

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

A) what color the star is
B) the total amount of mass in the star
C) the star's apparent size (the size seen from Earth)
D) how much energy the star gives off each second
E) the elements she can see in the star's spectrum