GMAT Critical Reasoning (CR) | Re: New Critical Reasoning question bank by carcass

Hey carcass!

Could you elaborate on question 6 please? Although I realize (after reading the explanation) that the problem in this question is the scope shift from # of entries to 'Regularity' of entries (how consecutively you enter - as in an evenly spaced set :D ), i don't seem to understand why answer D is correct because it simply restates the conclusion. How can a conclusion be an argument's assumption?

Thanks in advance!