The Spectral Luminosity Class of the Star Spica Is B1 $\tau$

Multiple Choice

The spectral luminosity class of the star Spica is B1 V,and that of the star $\tau$ Ceti is G8 V.From this (with luminosity measured in solar luminosities) ,we know for sure that

A) " $\tau$ Ceti is hotter but has the same luminosity as Spica."
B) " $\tau$ Ceti is cooler but has the same luminosity as Spica."
C) " $\tau$ Ceti is cooler and has a lower luminosity than Spica."
D) " $\tau$ Ceti is hotter and has a lower luminosity than Spica."