Let me knock this one out since no one has done it yet.
This is a flaw question so we'll start by identifying the argument core:
Law firm of S, P, and Associates if one of the most successful frims whose primary specialization is criminal defense cases.
Dalton is an attorney whose primary specialization if in divorce
Conclusion: Dalton certainly cannot be a member of S,P, and Associates.
The issue with this argument assumes that because the law firm has a difference specialization than Dalton, he can't be a member. Maybe the firm has a special divorce division lead by Dalton (think like a debater).
A. no internal contradiction here.
B. the author does not need to consider this.
C. let's break down the language. concludes that someone (Dalton) is not a member of a group (firm) on the grounds that that person (Dalton) does not have a characteristic (criminal defense spec) that the whole group(firm) has.
This is the flaw. Just because he doesn't have that characteristic, it doesn't mean that he cant be a member of the group. This is known as the whole/part flaw.
D. nothing about how evenly divided success is.
E. No issue with sample size being representative here, we are talking about Dalton and the law firm.