This a logical structure question. Why, it asks, does the author mention Poland? The answer lies in these lines: "On a theoretical level, it may be useful to strip away these concepts to more closely examine certain other dynamics at work, but the Marxist view often fails to describe what actually happens in the real world.
Consider the strong nationalism evident in Poland, even after generations of one party Communist rule." Poland is an example of how the Marxist view "fails to describe what actually happens in the real world," which is whatchoice D says.
Choices A and B are wrong because the purpose is not to discuss Communism.
Choice C is the opposite of what the passage says.
Choice E goes too far because the example doesn’t necessarily prove anything.