Hey suri84:

Good question - and for questions like these that ask for an assumption or presupposition upon which the argument depends, it's often helpful to consider the impact of the OPPOSITE of the answer choices. After all, if the argument depends on that statement, then the opposite of that statement should attack the argument.

With answer choice E, the correct answer, the opposite is:

It is NOT possible to classify a marketing decision properly as right or wrong

In this case, she then doesn't have a point at all - she cannot conclude that "half of the decisions were correct" because there is simply no way to know whether the decision was correct or incorrect. Because the opposite of the statement directly attacks her argument (and basically ruins it), then we can tell that the statement itself is necessary.


Choice D, when negated, is:

Marketing decisions are NOT just as likely to be correct/incorrect

Here this opposite would actually strengthen her argument somewhat, as her point is that the decisions were "only" right 50% of the time as though that was surprising. In either case, though, the general statistic of how often decisions are right/wrong isn't really applicable here - the conclusion is specific to her particular clients and their decisions. So whether the typical ratio is 50-50 or 20-80, neither would change the fact that her particular hit rate is 50-50. That's why D is irrelevant, and E is the correct answer.