How will the right answer fit in terms of support and conclusion?

Only the right answer will explain that this isn’t really a “counterexample”.

Highlight the main conclusion in the passage, if there is one:

There is no conclusion in the passage. You can think of the prompt implying the conclusion that there’s an “apparent counterexample”.

[BACKGROUND]. But [BACKGROUND].

Prompts that ask for an explanation like this almost always have a passage that makes a comparison. You should expect the right answer will map to the same comparison between “countries that have a stable political system” and the “unrest” in Athens.

Map the wording of the answers to the wording of the passage:

(A) …have in various ways been different…

That is so super generic, it can’t really help explain anything. This doesn’t compare “stable” and “unrest” or say anything about “intellectual progress”. No way you picked this unless you added in your own reasoning, which is not allowed.

(B) …generally held in high esteem…

This doesn’t help the comparison, since we have no idea if this is also true in “stable” countries. And it’s bringing in a new subject that isn’t obviously related to making “intellectual progress”.

(C) …typically unavailable in unstable political environments, but in ancient Athens…

You see how this goes out its way to connect the dots for us? It’s obvious that “financial support” helps explain why the Athenians “made unparalleled intellectual progress”. Aaand it does it in the context of the comparison between “stable” and “unstable” countries.

(D) …lead to stable political environments.

The passage doesn’t say anything about what causes “stable” environments, only that “intellectual advances” usually happen there. This doesn’t help explain what’s up with Plato and Aristotle.

(E) Many thinkers besides Plato and Aristotle…

…never get mentioned. You’d better have a clear and obvious reason why info about them explains the facts in the passage. Buuut you don’t. This tells us nothing about the comparison between making progress in a “stable” country versus a place where there’s “unrest”.

(C) is the correct answer.