Guys the answer should be D, because the argument implies that investigators have to find not just a cause of the event, but also a solution in order to make flights safer. The argument doesn't say anything about possibility to retrain pilots, maybe it is impossible, and even retrained they will do the same errors, we don't know! Maybe the changes will have effect only on new generation pilots... But finding the cause the investigators will anyway contribute to changes, and make these flights safer.
So,
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So,
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