Consultant: Ace Repairs ends up having to redo a significant number of

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?

Passage Map: Chronologically, it looks like -
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, - A reasoning to make a claim. It is established that mechanics who do initial repairs and mechanics who redo unsatisfactory jobs are equally capable to do their job.

we must reject the hypothesis that mistakes made in the initial repairs are due to the mechanics' lack of competence. - This is the claim, based on previous reasoning, that mechanics' lack of competence is not the reason behind mistakes in initial repairs. This is the main conclusion.

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. - BF1: Since we have a few assumptions previously established, this is paradoxical finding that is author tries to resolve in the passage ahead.

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. - The keyword 'rather' suggests that author takes a turn to explain the issue at hand. 'it is likely' suggests that whatever comes next is the possible reasoning given by author. Here author clears the ambiguity as presented in BF1 by giving a alternative explanation as why was that so.

A. The first is the consultant's main conclusion; the second provides evidence in support of that main conclusion. - WRONG. An easy elimination since both parts are incorrect. Neither BF1 is main conclusion, nor BF2 is 'evidence'.

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. - WRONG. First part is wrong since BF1 is neither an 'evidence' nor it serves as the 'basis' to reject anything. Second part is correct - BF2 is consultant's explanation.

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. - WRONG. First part is wrong to say that BF1 is a 'claim', neither it's the issue of its truthfulness - finding its truthfulness may result in either way, it may be true or may not be. Second part is wrong to say that BF2 acts as an 'evidence' and also wrong in saying what BF2 does.

D. The first presents a contrast whose explanation is at issue in the reasoning; the second is the consultant's explanation of that contrast. - CORRECT. First part is correct. If we follow the chronology of passage we find that BF1 present an opposite(to assumption) finding which is an issue at hand. Second part is also correct for BF2 is consultant's explanation.

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. - WRONG. First part is correct about BF1. Second part is wrong for neither BF2 is an 'evidence' nor it challenges anything at all in the passage.

Answer D.