Thanks for the question. A couple of things here that might help. First, this is an Assumption question, and you can see all sorts of levels of language regardless of what you see in the stimulus. That's actually also true for any question because of the different ways things can be phrased, although, in many First Family questions you see weaker language in the answers if the stimulus contains weak language. However, question types aside, in looking at the stimulus here, you see plenty of strong language ("cannot be...unless" and "shifts...detract from the merit").
Second, let's look more closely at the critic's argument. There are different ways to view this argument, but the first sentence is conditional, so I'll place it in those terms:
Premise: Novel highest quality
Most readers emotionally engaged
Premise: Narrative shifts
Tend to focus on author
Conclusion: Narrative shifts
Detract from work
Answer choice (C) is:
Premise: Tend to focus on author Most readers emotionally engaged
Do you see how (C) operates as a Supporter Assumption? It is connecting pieces of the argument.
Please let me know if that helps. Thanks!