According to rational-choice theory, popular support for various political parties can be explained sufficiently in terms of deliberate decisions by individual voters to support the party whose policies they believe will yield them the greatest economic advantage. This theory is opposed by many sociologists on the grounds that a complex phenomenon such as the rise of a political organization cannot be caused by a simple phenomenon.
It can be properly inferred from the statements above that many sociologists believe thatThe sociologists reject rational-choice theory because they think it explains a complex political phenomenon by appeal to something too simple.
So they must regard economically motivated voter decisions as at least potentially simple, not automatically as a complex enough explanation.
(A) economically motivated decisions by voters need not constitute a complex phenomenon
This is correct. The sociologists object that a complex phenomenon cannot be caused by a simple phenomenon. Since the theory explains political support through economically motivated voter decisions, the sociologists must see those decisions as something that
need not be complex.
(B) a complex phenomenon generally will have many complex causes
This is too strong. The passage says they reject a simple cause for a complex phenomenon. It does not say complex phenomena generally have many complex causes.
(C) political phenomena often have religious and cultural causes as well as economic ones
This may be plausible, but it is not stated or required by the passage.
(D) popular support for political parties is never a complex phenomenon
This is the opposite of the passage. The sociologists treat the rise of a political organization as complex.
(E) the decisions of individual voters are not usually influenced by their beliefs about which policies will yield them the greatest economic advantage
This is not supported. The sociologists reject the theory as a sufficient explanation; they do not deny that economic beliefs influence voters at all.
Answer: (A)