nocilis wrote:
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. For only then can changes be made to ensure that the same type of error does not recur and cause another accident.
Which of the following is a presupposition of the argument above?
(A) Pilot error is not a contributing factor in most airline accidents.
(B) Airline companies themselves should be the agents who investigate airline accidents.
(C) Stricter government regulation of airline companies will make air travel significantly safer.
(D) Investigators of airline accidents should contribute to the prevention of future accidents.
(E) Most pilots who make errors in flying will repeat their errors unless they are retrained.
In the second sentence, notice the use of "For" only then ... It plays the role of "because". It marks a premise, not a conclusion.
Premise:
Only when one finds out why the error was made by analyzing A, B and C, can changes be made to ensure that the same type of error does not recur and cause another accident.
Conclusion: Instead of blaming an airline accident on pilot error, investigators should find out why the error was made by analyzing A, B and C
What is the gap in the argument? The premise tells you that only when you do X, will future accidents be avoided. The conclusion says that investigators should do X.
The assumption is that investigators should help in preventing future accidents. That is why the author asks them to do X.
Add this assumption to the argument and see if it makes sense:
Only when you do X, will future accidents be avoided.
Investigators should help in preventing future accidents.
So investigators should do X.
Makes sense now, right? So (D) is correct.
As for (E),
The argument asks investigators to analyse the training program, not retrain the pilots. Nothing has been said about pilots needing retraining. Perhaps analysis of training program will reveal that pilots are taught in a different way whereas airplane design shows it differently etc. Then it is a judgment call on whether pilots need to be retrained or airplanes need to be redesigned. All I mean to say is that perhaps pilots don't need to be retrained. Our argument certainly does not assume it. IT asks us to analyse multiple things to avoid errors in the future.