In an H-R Diagram, Where Can You See the Spectral

Multiple Choice

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example) ?

A) along the right (vertical axis)
B) along the bottom (the horizontal axis)
C) only in the red giant region
D) only on the main sequence
E) H-R diagrams have nothing to say about spectral types