In the Self-Propagating Star Formation Theory

Multiple Choice

In the self-propagating star formation theory

A) spiral arms are formed and sustained primarily by the actions of solar-mass stars because there are so many more of them than there are high-mass stars.
B) spiral arms are poorly defined because they are formed and sustained primarily by the actions of short-lived massive stars.
C) the passage of dust clouds through the spiral arms triggers star formation.
D) spiral structure results with thin, well-defined arms.