Explanation

Reading the question: we dig into the argument. This question doesn't have much to do with the governor; just a four-year period. Sales are up over the last four years, but credit paid off was higher for two years and then much lower for two years. We need to explain 1) the drop in credit paid off on time. Above all, the correct explanation will accommodate the fact 2) sales have been up. We can use that simple fact as a basic relevance filter.

Applying the filter: (A) doesn't address explicitly or implicitly the fact that sales are up, so it doesn't pass the filter. Choice (B) is an anti-explanation; if costs went down in the latter two years, it should have been easier to pay off credit. Choice (C) is an explanation. It connects to both 1) and 2). We might have imagined that the body of dealerships was unchanging the whole time, but the argument didn't actually say that. Choice (D) ends up saying nothing because it only hints at a possible future outcome, not something affecting the last two years. (E) at least discusses credit and involves a change between the first two years and the second two years. But most likely extending less credit would lead to getting more of it paid off on time, not less. It's also unclear from (E) whether the credit is due during these periods, because we care not so much about when it's extended as whether it's paid when due during one period and the next. So (E) is out. The correct answer is (C).