The author’s argument isn’t flawed due to sample size. 600 is simply referring to the number of the largest corporations in North America, and the conclusion is about these same “most important” corporations. She isn’t using an unrepresentative sample to draw her conclusion.

Just because a small percentage of people from service professions are board members, does not mean that a small percentage of board members are from service professions. The author mistakenly assumes that it does.

The author doesn't make this mistake because she isn’t talking about corporate boardrooms generally. She’s just talking about “the most important corporate boardrooms in North America.”

How this impacts smaller corporations is irrelevant. The argument only addresses the largest corporations in North America.

The author never addresses corporations’ levels of social responsibility or how board members from service professions might impact social responsibility. (E) is irrelevant.