While Sirius, the Dog Star, is type AO, a start just a step hotter than M0 is a related what?
A.M1
B.K9
C.F5
D.AOK
E.B9
B. K9
K9 is followed by M0 in the temperature/spectral classification of stars. K's are hotter than M's, and K9 is the coolest of the K's