Identify the subject in “but a thin train of dust was left in the air”

What is the central idea of the "allegory of the cave"? a. most men live chained to the wall of a cave all of their lives, facing a blank wall, and trying to guess the nature of objects reflected by a fire. b. a philosopher is like a prisoner freed from the cave that comes to understand that the shadows are not reality, rather he understands reality by his experience. c. men who allow their experience to be shaped by perceptions and shadows do not know a better life. d. a philosopher must return to share the news of enlightenment with others who will not necessarily accept his good news. part