What I gathered from this question and Manhattan question (
https://gmatclub.com/forum/top150-cr-in ... 05980.html, don't know which is original):
Simple change of one word changes the conclusion and hence the answer. In presupposition/assumption you have to always identify the conclusion to help in POE. Here, second line isn't the conclusion. But rather the first line is the conclusion:
Quote:
Instead of blaming an airline accident on pilot error, investigators should find out why the error was made by analyzing airplane design, airline management, and pilot-training programs.
With this conclusion let's analyze why negation of E isn't correct:
Quote:
Most pilots who make errors in flying will not repeat their errors unless they are retrained.
Even if pilots don't repeat their mistakes, the conclusion isn't breaking. It doesn't change the fact that investigators should still find out the errors made by other pilots(pilots who never made errors and making their first error) or errors related to airplane stuff. They still have to investigate that. This option doesn't change anything.
Negation of D on the other hand:
Quote:
Investigators of airline accidents shouldn't contribute to the prevention of future accidents.
If they shouldn't contribute to the prevention of accidents, then whole conclusion of them finding out errors doesn't stand a chance. Premise is "we need to find out errors to contribute to the prevention of accidents" but if investigators themselves aren't interested in that then whole argument falls. This is SUFFICIENT and hence this is the correct answer.
Now coming to the Manhattan Question:
Subtle change: (from for only then to only then)
Quote:
Only then will the insurance companies be able to effectively issue guidelines to prevent future accidents, instead of merely punishing the incidental driver.
And this change makes this above line our conclusion. And hence in the similar options given to us we have to choose E here instead of D.