One Difficulty with the Density Wave Theory Is That

Multiple Choice

One difficulty with the density wave theory is that

A) the theory fails to explain why a given spiral pattern lasts only a small fraction of the lifetime of a galaxy.
B) the theory fails to provide a mechanism for star formation.
C) astronomers are unsure of the mechanism that produces the energy output necessary to sustain the density wave.
D) the theory fails to explain the distribution of Population I and Population II stars in the galaxy.