GWD28-38 选A or D?

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.

选A，假定条件是前后两种机修工的水平都一样，所以只是工作态度差别了。

D稍离题远些，找不到处罚的信息，有太多的可能。

D若取"非",重修會對技工不利,則不是也導不出結論嗎?

要如何刪除此選項呢?