@Crystal it is important to keep in mind that this is not a Must Be True question so the fact that the stimulus does not state that large cities are heavily populated does not rule out (E) as the correct answer choice.
This is a Paradox question so we are looking for the answer choice that serves as a possible explanation for the discrepancy in the stimulus.
And what is the discrepancy? That ancient Romans understood the principles of water power very well and made extensive use of water as an energy source in some outlying parts of their empire but did not do so in regions dominated by large cities.
So we are effectively looking for a plausible explanation as to why ancient Romans did not use water power in regions dominated by large cities but did do so in some outlying parts.
(E) serves a a possible explanation for this discrepancy by introducing a consideration that could explain the ancient Romans decision not to use water power in regions dominated by large cities, i.e. in heavily populated areas the introduction of water power would have been certain to cause social unrest by depriving large numbers of people of their livelihood.
(A) is incorrect because it does not serve as a possible explanation for the discrepancy in the stimulus. In fact, one could argue that the information in (A) makes the non-use of water power in regions dominated by large cities even more perplexing (since they were capable of transporting water sufficient to supply large cities over considerable distances).
Hope this helps! Please let us know if you have any other questions.
Ashley-TienJuly 10, 2018
Why is B incorrect?
ChristopherJuly 30, 2018
@Ashley-Tien, the information in (B), while possible, doesn't help to resolve the apparent paradox.
For one thing, there is nothing to suggest that in the outlying parts of the empire there were not seasonal variations in water-flow. Also, if the ancient Romans "understood the principles of water power very well," then they likely would have been able to overcome some seasonal variation if there was considerable flow most of the time.
Also, for a large city to exist in ancient times would have required a significant water source, so you're looking for an explanation that would explain why the Romans were not using water power despite its availability. Saying that the flow of those water supplies was somewhat seasonal doesn't help resolve that paradox.
