A significant number of complex repair jobs carried out by Ace Repairs have to be reworked under the company’s warranty. The reworked jobs are invariably satisfactory. When initial repairs are inadequate, therefore, it is not because the mechanics lack competence; rather, there is clearly a level of focused concentration that complex repairs require that is elicited more reliably by rework jobs than by first-time jobs.

The argument above assumes which of the following?

1. There is no systematic difference in membership between the group of mechanics who do first-time jobs and the group of those who do rework jobs.

2. There is no company that successfully competes with Ace Repairs for complex repair jobs.

3. Ace Repairs’ warranty is good on first-time jobs but does not cover rework jobs.

4. Ace Repairs does not in any way penalize mechanics who have worked on complex repair jobs that later had to be reworked.

5. There is no category of repair jobs in which Ace Repairs invariably carries out first-time jobs satisfactorily.

这题看了前人的讨论，又反复读了N遍仍然百思不得其解，主要问题有2：

1.E选项怎么翻译？

2.如果将A选项取非，并不能直接使原结论不成立，因为虽然A说两个系统工人不同，但是没有说清是什么不同，即使默认为是技术能力不同，那也没说谁高谁低呀。。。如果first-time job的工人能力高，那不是加强了结论吗？

迷惑～～求解！