Cotrell is, at best, able to write magazine articles of average quality.
Conclusion (avg quality = opinion)
Cotrell can at best write articles of average quality.
Intermediate conclusion
Cotrell must have plagiarized the few articles submitted by him that are of superior quality.
Evidence (since)
Cotrell is incapable of writing an article that is better than average.
Evaluate
This is certainly a weird argument. The author is trying to prove that Cotrell is a mediocre/poor writer, and the most compelling evidence for that are these articles submitted by Cotrell that are of superior quality?
That makes no sense. How are superior quality articles evidence that Cotrell is an average to poor writer?
The author says, "Because Cotrell plagiarized those articles". To which we should react, "Oh? How do you know Cotrell plagiarized them?"
To which the author says,
This should make us feel like we're right back at the start, because this is a Circular argument. Of the 10 famous flaws, Circular might show up the most in answer choices, although it's almost never correct. So enjoy this rare treasure. :)
It refers to an argument in which a premise restates the conclusion or requires the conclusion to be true. In this argument the premise restates the conclusion, .
Goal
Look for an answer choice calling out the Circular Reasoning or otherwise making the complaint that the author seems unfairly confident that Cotrell plagiarized these superior articles. Her only premise for thinking he plagiarized the good ones is her pre-conceived notion that he's not capable of writing superior articles.