What Is One of the Differences Between Cepheids and RR

Multiple Choice

What is one of the differences between Cepheids and RR Lyrae variables?

A) Cepheids are giants, but RR Lyrae stars are still on the main sequence.
B) All Cepheids have the same brightness, but RR Lyrae stars vary greatly in luminosity.
C) The period-luminosity relation holds only for RR Lyrae stars.
D) The pulsations of RR Lyrae stars are much less regular than those of Cepheids.
E) The RR Lyrae stars have much shorter periods than Cepheids.