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

Only the right answer will complete the conclusion started in the prompt, a conclusion that’s guaranteed by support in the passage.

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

There is no conclusion in the passage. The conclusion started by the prompt is “many sociologists believe that…”, which the right answer will complete.

[SUPPORT]. [SUPPORT].

The author changes the subject between the first and second sentences. The implication is that the “complex phenomenon” and the “simple phenomenon” mentioned in the second sentence are references to “popular support for political parties” and “decisions by individual voters”, respectively. But the author didn’t actually say that, so the right answer is likely to spell out that connection.

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

(A) economically motivated decisions by voters need not constitute a complex phenomenon.

The wording is unclear on purpose, but you’re expected to recognize that this says that voters’ decisions could be called a “simple phenomenon”. That’s part of what the author implied. And this answer didn’t bring in anything new or use really strong wording, so you’re not eliminating this one.

(B) …will have many complex causes

This is tricky, but this wording doesn’t actually map. The author said “cannot be caused by a simple phenomenon”, so that means the cause has to be either complex, or more than one thing. This answer says it has to be both, which is a much stronger statement this passage doesn’t actually support.

(C) …often have religious and cultural causes…

This is bringing in new wording the author doesn’t use or make any direct reference to.

(D) …is never a complex phenomenon

Whoa, too strong. The author doesn’t say anything strong enough to support a conclusion that uses “never”. And if you think about it, this actually contradicts their argument, since they implied that “the rise of a political organization” is complex.

(E) …are not usually influenced by…

This is misquoting the sociologists. They oppose the theory, so they don’t think popularity of political parties is “explained sufficiently” by voters’ beliefs. But that doesn’t mean they think those beliefs don’t “influence” voters’ decisions.

(A) is the correct answer.