Why Does the Cepheid Distance Method Fail Us Beyond About

Multiple Choice

Why does the Cepheid distance method fail us beyond about 20 Mpc?

A) The intergalactic dust reddens the Cepheid's light and apparent brightness.
B) Distant galaxies are seen in the past, and Cepheids evolve with time.
C) The periods of Cepheids grows longer as the distances increase.
D) Distant galaxies are younger than our Milky Way; too young to have Cepheids yet.
E) Even with the HST, the most luminous Cepheids are too faint to be seen beyond 20 Mpc.