The question states, "The quotation in lines 21-23 suggests that Barbu assumes which one of the following about Aeschylean drama?"
We're looking to find an assumption that Barbu is making in his argument. In the text, we see that the quotation is about Barbu using Aeschylean drama to prove a contention about ancient Greek civilization and an individual's place within it. This is very similar to a part-to-whole flaw; in using Aeschylean plays as support, Barbus is making the assumption that Aschylean drama was fully representative of ancient Greek society. Let's look for an answer that captures our anticipation.
You asked about (B).
(B) says, "Aeschylean drama introduced new ways of understanding the role of the individual in ancient Greek society."
We know that Aeschylean drama provided support for the new view of the role of the individual in Greek society, but we do not know whether it introduced it. It could have been introduced by something other than Aeschylean drama. Barbu is not assuming that Aeschylean drama introduced this concept, so we can get rid of this answer choice.
(D) says, "Aeschylean dramas accurately reflect the way personal autonomy was perceived in ancient Greek society."
(D) is precisely what we're looking for. We know that Barbus is assuming that Aeschylean dramas were representative of ancient Greek society, so this is the correct answer choice.
Does this make sense? Let us know if you have any questions!