Cotrell is, at best, able to write magazine articles of average quality. The most compelling pieces of evidence for this are those few of the numerous articles submitted by Cotrell that are superior, since Cotrell, who is incapable of writing an article that is better than average, must obviously have plagiarized superior ones. The argument is most vulnerable to criticism on which one of the following grounds? ['It generalizes from atypical occurrences.', 'It infers limits on ability from a few isolated lapses in performance.', 'It presupposes what it seeks to establish.', 'It simply ignores the existence of potential counterevidence.']