What does the Hertzsprung-Russell Diagram NOT plot?

Question

A. temperature and mass

B. spectral class and absolute magnitude

C. absolute magnitude and luminosity

D. spectral class and temperature

Is it B?

Answer 1

Nope, of course not.
http://astrosun2.astro.cornell.edu/academics/courses/astro201/hr_diagram.htm

Answer 2

So A?

Answer 3

It was A. Thank you!