Explanation
The argument posits that the improvement in the Lalolah River's pollution ranking is evidence that the cleanup efforts are effective. However, the argument assumes that the change in rank corresponds to an actual reduction in pollution, rather than changes in the pollution levels of other rivers or changes in how the rankings are determined.
A. The argument does not interpret a lack of evidence for one claim as support for another; it assumes that a change in rank indicates effectiveness of cleanup efforts.
B. The flaw is not identified as a reliance on the term "most polluted," but rather in the assumption about what the change in ranking indicates.
C. While the basis for the ranking is not disclosed, the flaw concerns the assumption made about the effectiveness of cleanup measures, not the transparency of the ranking system.
D. The argument does not confuse the state of individual rivers with the district as a whole; it specifically refers to the ranking of the Lalolah River.
E. (Correct Response) The argument equates a relative decrease in rank with an absolute decrease in pollution, which is flawed reasoning. The river could still be just as polluted, or even more polluted than before, but ranked differently if the other rivers have become more polluted or if the ranking criteria have changed.
Option E identifies the flaw in the argument by pointing out that a change in relative ranking does not necessarily equate to an absolute improvement in the river's condition.