The stimulus tells us that a bunch of new apartments have been built in Brewsterville. Usually, this would lower the rents for existing apartments. However, in Brewsterville, the rents for existing apartments went up.
We're looking for an answer that helps us explain this discrepancy. The discrepancy we're searching for is between what is generally the case and what happened in Brewsterville. Normally rents of existing buildings fall, but in this case they rose. We need an answer that provides us with an explanation that is about something specific about Brewsterville that'd make its older apartments become more expensive even after the new apartments were built.
(E) says, "The new apartments were constructed at the outset of a trend of increasing numbers of people seeking residence in Brewsterville."
Even if building new apartments generally reduces older apartment buildings' rents, this may not have happened in Brewsterville because more people, in general, were moving there. This answer choice helps resolve the paradox because there are simply lots more people moving to the town, which helps explain why rents in older buildings would still be going up since demand is still increasing. Thus, (E) is the correct answer choice.
Does this make sense? Let us know if you have any more questions!