gmat prep top managers

It's E.

In order to confirm that intuition is more effective than methodical reasoning through the fact that top managers use it more often than middle/lower managers we must assume that top managers are more effective than middle/lower managers.

In D, we don't need to assume that top managers use intuition for the majority of their decisions, since we already know that they use intuition significantly more, it doesn't matter exactly how much more or what percentage more. What it matters is that they (top managers) are more effective so we can conclude that intuition is more effective than methodical reasoning.

Its E

IMO E. An assumption is helpful to find or form a conclusion. So, try plugging in the assumptions before conclusion and see whether it helps. If its helping to form a conclusion (the one we already have), then thats the right answer.

I feel the answer will be E.