Stadium owner: While I respect the right of local businesses to voice their opinions, I find their complaints about the traffic around our venue to be completely unfounded. Large stadiums always attract traffic when there are events, and our venue was built for both sporting events and major concerts, so those businesses should have taken that into account when choosing to locate.

Here the only reason why the stadium owner is disregarding the complaints is that the owner claims traffic to be a normal issue around such big stadiums and hence the owners should have taken this into account before opening a shop nearby stadium. Well, the only condition where this argument will break is if the shops were there before the stadium was built. If that is the case then the owners had no chance of taking this into account.

Which of the following is an assumption required by the stadium owner's argument?

(A) The flow of traffic has remained constant throughout the stadium's existence.
Not relevant. The complaint is not about the rate of increase in traffic.
(B) The stadium does not attract more traffic than other, similarly-sized venues.
Even if the stadium does, this does not explain why the owners didn't think about this while opening shops.
(C) The businesses that are complaining moved to the area after the stadium was built.
Correct
(D) The employees and customers of local businesses attend events at the stadium.
Not relevant.
(E) Not all events at the stadium attract a large volume of traffic.
That might be true but this does not affect the argument here.
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Stadium owner: While I respect the right of local businesses to voice their opinions, I find their complaints about the traffic around our venue to be completely unfounded. Large stadiums always attract traffic when there are events, and our venue was built for both sporting events and major concerts, so those businesses should have taken that into account when choosing to locate nearby.

Which of the following is an assumption required by the stadium owner's argument?

(A) The flow of traffic has remained constant throughout the stadium's existence.
(B) The stadium does not attract more traffic than other, similarly-sized venues.
(C) The businesses that are complaining moved to the area after the stadium was built.
(D) The employees and customers of local businesses attend events at the stadium.
(E) Not all events at the stadium attract a large volume of traffic.

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VERITAS PREP OFFICIAL SOLUTION:

Notice the specific wording in the stadium owner's position: businesses should have considered the stadium when choosing to locate nearby. You might anticipate simply from that "what if the businesses were already there?" But even if you didn't, you can use the Assumption Negation Technique on choice C: if the businesses relocated to the area BEFORE the stadium was built, then they have every right to complain. The stadium brought new traffic that they did not expect! Choice C is therefore correct.

Assumption Negation helps to show that the other choices do not directly impact the owner's position. Even if the flow of traffic was not constant (the opposite of A), you could still argue that the businesses should have known to expect high traffic volume overall. Similarly, B is irrelevant: even if the stadium attracts more traffic than similar stadiums, that does not rule out the premise that "you should know stadiums will attract traffic, and therefore take that into consideration if you move your business nearby." E is very similar: again, even if all events at the stadium attract a lot of traffic, that doesn't undermine the point that businesses could have planned for it. And choice D is completely irrelevant: whether the employees benefit or not has nothing to do with whether one can complain about the traffic's impact on business.
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This is an apt and easy example to understand pre thinking in CR.
While reading the question statement itself you can frame an assumption that conclusion is built on an assumption that all shops opened post the construction of the stadium.