It Was Discovered That Stars of the Same Temperature Can

Multiple Choice

It was discovered that stars of the same temperature can include stars of different radii. The response to this finding was

A) to refine the spectral classification scheme by introducing subheadings 0-9.
B) to revise the spectral classification to start with O rather than A.
C) to define the luminosity classes.
D) to invent the H-R diagram.