Very very good and easy question.
THE ANSWER IS E AND E ONLY.
Explaination :- Questions asks us what is the "pre-supposition. It means what ASSUMPTIONS were made while reaching the conclusion"
There are 2 techniques to find the Assumption
1) ASSUMPTION NEGATION :- First find the premise and conclusion of the argument. Then negate answer choices only by one. The answer choice which after negation makes the conclusion weak is the correct answer. THIS IS THE TECHNIQUE MOST PEOPLE USE TO FIND ASSUMPTION
2) ASSUMPTION ADDITION :- Assumption is a premise that is not written or expressed in the argument. But assumption is an important premise to reach the conclusion. In this type of questions a strong unstated assumption is always present in the option choices that when inserted in the argument make it complete. So in this technique you add one of the OPTION from answer choices as a Premise just before the Conclusion. The answer choice that makes the argument complete is correct.
NOW LETS GET TO THE BRASS TACKS (BRASS TACKS is an idiom that means "focus on the issue in hand"

)
We will use ASSUMPTION ADDITION technique.
First we will have to quickly identify and isolate the PREMISES and CONCLUSION of the argument.
Premise 1) Don't blame pilot for accidents.
Premise 2) Investigate why error was made by analysing these areas :- airplane design (X), management (Y), and PILOT TRAINING PROGRAM (Z)
Premise 3) ----HERE WE WILL ADD THE ANSWER OPTIONS A,B,C,D,E --ONE BY ONE-----
Conclusion) Only after making changes in design, management and pilot's training we can ensure similar type of accidents does occur in future
SO add option E in place of PREMISE 3 and see how the argument becomes fool proof, cogent and strong.
Premise 1) Don't blame pilot for accidents.
Premise 2) Investigate why error was made by analysing these areas :- airplane design (X), management (Y), and PILOT TRAINING PROGRAM.
Premise 3) (E) Most pilots who make errors in flying will repeat their errors unless they are retrained.
Conclusion) Only after making changes in X, Y and Pilot's training(Z) we can ensure that similar kind of accident does occur in future
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.
(Reverse answer. Pilot training is the most important factor)
(B) Airline companies themselves should be the agents who investigate airline accidents.
(Irrelevant to the issue)
(C) Stricter government regulation of airline companies will make air travel significantly safer.
(Out of scope)
(D) Investigators of airline accidents should contribute to the prevention of future accidents.
(There is a possibility that investigators have already contributed to the prevention of accidents by filtering out the possible reasons for the accident. Investigators may have given a detailed report to Airline management explaining the cause of the accidents but the managment decided not to implement the recommendation from the investigators because it will require large amount of investment and decline airline's profit margin. So we don't know whether investigators are or not contributing. No information in the argument to validate this option)
(E) Most pilots who make errors in flying will repeat their errors unless they are retrained.
(yup correct answer :- Don't blame pilots for accidents. you don't gave them proper training. An inexperienced pilot will keep causing accidents unless you train him properly.)