The passage tells us that some scientific issues are too complex to be understood by popular magazine readers, even though readers would find these issues the most fascinating. It then concludes that these issues are not covered in popular magazines.
We are tasked with completing the passage by selecting the answer choice that explains why the conclusion (that these complex but fascinating issues are not covered in popular magazines) was drawn.
Answer choice (C) states that "highly complex and counterintuitive theories are increasingly common in almost all branches of science." This answer choice is incorrect because it is irrelevant. It has nothing to do with magazine readers or explaining why the stories are not run in popular magazines. Since it does not connect the premises to the conclusion in any clear way, it should be eliminated.
Answer choice (A) states that "editors of popular magazines generally do not approve stories about issues that cannot be well understood by those magazines' readers." This provides a reason for the issues not being covered in popular magazines, thereby supporting the conclusion and connecting it to the given premises.
Does that make sense? Please let us know if you have any additional questions!