Consultant: Ace Repairs ends up having to redo a significant number of the complex repair jobs it undertakes, but when those repairs are redone, they are invariably done right. Since we have established that there is no systematic difference between the mechanics who are assigned to do the initial repairs and those who are assigned to redo unsatisfactory jobs, we must reject the hypothesis that mistakes made in the initial repairs are due to the mechanics’ lack of competence. Rather, it is likely that complex repairs require a level of focused attention that the company’s mechanics apply consistently only to repair jobs that have not been done right on the first try.

In the consultant’s reasoning, the two portions in boldface play which of the following roles?

A. The first is the consultant’s main conclusion; the second provides evidence in support of that main conclusion.
B. The first is evidence that serves as the basis for rejecting one explanation of a certain finding; the second is the consultant’s own explanation of that finding.
C. The first is a claim whose truth is at issue in the reasoning; the second provides evidence to show that the claim is true.
D. The first presents a contrast whose explanation is at issue in the reasoning; the second is the consultant’s explanation of that contrast.
E. The first presents a contrast whose explanation is at issue in the reasoning; the second is evidence that has been used to challenge the consultant’s explanation of that contrast.

D