A. The first states the conclusion of the argument; the second calls that conclusion into question.
By looking at the structure of the passage it seems ok. I'll leave it here for now.
B. They are both claims, each stating the exact opposite of other.
I wouldn't call it a claim also the second seems to be calling the first into question because of the research test group used. It seems to be saying that "hey, your conclusion is a generalisation because majority of the entrpreneurs are above forty and so and so" so it is NOT saying the opposite. INCORRECT
C. The first is part of a conclusion which the second challenges.
Seems quite similar to the option A. I'll keep it for now.
D. The first is evidence that has been used to support an explanation that the argument challenges; the second is contradictory evidence.
The second is definitely not contradictory evidence. It is just evidence that may havr been ignored by the ignored by the research - INCORRECT
E. Each calls into question the conclusion of the argument.
If each call the conclusion into question, where is the conclusion? Most definitely INCORRECT
Between A and C if you look closely the study concludes things: potential entrepreneurs can be encouraged or discouraged by business school programs, and new ventures by entrepreneurial alumni make tremendous case-study materials for entrepreneurial courses.
Only the first part (before and) is bolded so option C fits best.
Hope this helps!
Posted from my mobile device