Cary is, at best, able to write poems of average quality. The most for

Cary is, at best, able to write poems of average quality. The most forceful pieces of evidence for this are those few of the numerous poems submitted by Cary that are superior, since Cary, who is incapable of writing a poem that is better than average, obviously must have plagiarized the superior ones.

The argument is most vulnerable to criticism on which of the following grounds?

A. It simply doesn’t take into account the existence of potential counter- premise : Incorrect. There is no such counter-premise that the argument does not consider.
B. It generalizes from one of its kind occurrences. : Incorrect. There is no such mention that cary has plagiarized before.
C. It presumes what it seeks to establish. Correct : the argument presumes that since cary cannot write above-average poems, she must have plagiarized.
D. It depends on the judgment of specialists in a matter where their specialty is irrelevant. Incorrect. no such mention of a specialists.
E. It infers limits on ability from a few standalone lapses in performance. Incorrect : the argument does not mention whether there were a few lapses in performances in Cary's poems.

He is using the conclusion as the premise for the reasoning why Cary's poem writing is average.

Conclusion - Cary's poem writing is average
Premise - His poem writing is average because he has few poems that are superior and because he is average he must have plagiarized those few.

Hope this helps