Explanation

Reading the question: this is a weak argument, and we're asked to weaken it, so it will end up in shambles. We can create a filter by making a prediction of the answer. Perhaps unemployment for this population fluctuates from year to year around some level, so it's not down, it's basically the same within the envelope of fluctuation. We can use that expectation to filter the answer choices.

Applying the filter: choice (A) would strengthen the argument, so it's out. Choice (B) bears some similarity to our prediction, so it passes the filter. Choice (C) presents a hypothetical that does not shed light on the truth of the current situation, so it's irrelevant. Choice (D) doesn't especially weaken the argument; the rate could still be on a downward trend, given (D). Choice (E) is a definition of the unemployment rate that doesn't shed light on whether it's truly downward-trending. That leaves us with choice (B).

Logical proof: We can confirm choice (B) with the negation test. What if this year a temporary government spending project increased the unemployment rate by 0.8 percent? Then we have a reason to believe that the rate will go down in the future, when the temporary project effect is gone. So the negation of (B) would strengthen the argument, so (B) itself does weaken the argument. The correct answer is (B).