Conclusion: That criticism, like so many other criticisms from the same source in the past, is completely unwarranted, as anyone who has actually read the novel would agree.
Reasoning: Each one of the incidents in which Smith’s hero gets involved is the kind of incident that could very well have happened to someone or other.
Task: determine the most serious
error of reasoning in the argument. Important to note that you're to find the error in the reasoning, not the conclusion.
(A) It relies on the assumption that a criticism can legitimately be dismissed as unwarranted if it is offered by someone who had previously displayed questionable judgment. We're supposed to find the error in the reasoning, not the conclusion.
Rejected.
(B) It ignores the fact that people can agree about something even though what they agree about is not the case. "Agreeing to disagree" - this is far out of the argument's scope.
Rejected.
(C) It calls into question the intellectual integrity of the critic in order to avoid having to address the grounds on which the criticism is based. The grounds were actually addressed.
Rejected.
(D) It takes for granted that a whole story will have a given characteristics if each of its parts has that characteristics. Addresses the reasoning - just because its incidents inhibited a specific characteristic, we can't generalize that for the story in its entirety.
Correct.
(E) It attempts to justify its conclusion by citing reasons that most people would find plausible only if they were already convinced that the conclusion was true. Not really, well out scope, and has nothing to do with the reasoning.
Rejected.