The question stem, "The passage can best be described as..." means we need to be looking at the passage as a whole. There may be certain elements that show up in answer choices, but we need to keep in mind the overall meaning and tone of the passage.
Let's look at the answer choices.
A) There is a discussion about this in paragraph four, but I would not say that it represents the whole passage.
B) Of the pros and cons of polyarchy listed in the passage, this is one of the cons. It is mentioned in paragraph three, as one of the criticisms levied against polyarchy in the 60's and 70's. It does not seem to represent the entire passage.
C) Again, this is something that is briefly mentioned in the passage, but does not characterize the passage as a whole.
D) This is is the correct answer, because it is a broader statement that fits the passage. Although it is focused on one author who defends polyarchies, the passage includes both support for polyarchy as well as criticism.
E) The relationship between political parties and pressure groups is mentioned as a force that maintains a functioning polyarchy, but the similarities between these groups are not the primary subject of the passage.
