Explanation

Reading the question: the argument is not exactly airtight; it can probably be attacked in a number of ways. Arguments on Critical Reasoning questions tend to be flawed, since the questions tend to ask us to identify flaws. But any argument, even a good one, is prone to attack, and more difficult Critical Reasoning questions will tend to feature better-constructed arguments.

Creating a filter: The question stem has the classic understated testmaker's language. We can prove by stronger terms and interpret the phrase "what's most useful for evaluating" as what's critical for evaluating. And we have another shortcut, since there's a causal argument here. It's in the last sentence, which roughly asserts that switching from exporting to importing lumber causes a city's forest to go away (presumably because they introduced insects). Our expectation is that there might be "another cause" of the export-import switch, but regardless, we'll look for something on which the argument depends.

Applying the filter: Do any answer choices deal with "cause of export-import switch"? (C) does and (E) might. Choice (C), now that we look closer, is one of our specific expectations; it's a causality flip; switching to imports didn't cause deforestation; rather, deforestation led cities to import lumber. That makes a tremendous amount of sense and, if true, would deal a major blow to the argument, because the truth about other cities would have no connection to the insects.

Logical proof: We apply the negation test. If (C) is negated, cities didn't make the switch to import because they were deforested. That possibility would strengthen the argument by removing a major problem. If we have time, we could confirm that the other answer choices are not material to the argument by considering them in negated form. The correct answer is (C).