Situation: Gracie’s theory about the unequal utilization of community property like river and lakes in comparison of private properties such as wells appeared to be unjustified, according to one study.
Reasoning: We need to select a question the answer to which would provide the most useful information for us to evaluate the findings in the study as they relate to Gracie’s thesis.
(A) Incorrect: Whether any citizen or citizens in the study used both common and private water sources makes no difference as far as our argument is concerned.
(B) Incorrect: Individual preference has no bearing on the results of the quality study.
(C) Correct: If the wells started off in significantly worse shape than did the lakes, then any comparison between the two is invalid and irrelevant. On the other hand, if everything started in the same condition, the decline in quality of the wells casts significant doubt on Gracie’s thesis. This information is key.
(D) Incorrect: Again, this is immaterial to the water sources’ quality.
(E) Incorrect: The mere fact of using public water sources tells us nothing of the reason for doing so; a well-owner might use the river to preserve her well, or she might do so because the well was tainted from the very first day it was dug. Without many more follow-up questions, this answer cannot be useful.
C is the correct answer.