Explanation

Reading the question: supposing we don't see a flaw, we can jump straight to a logical proof. The answer choices are not statements, so we can't negate them, but they can be evaluated by analysis by extreme cases to detect impact on the argument. Answer choices that represent variable ranges or amounts are suited to analysis by cases.

Logical proof: we look at (A). Extreme case: the owner has spent a lot of money on the current set. That doesn't impact the ability to save in the long run. We're more interested in how expensive they are relative to the cost of the new ones given how often the old ones need to be replaced and how often the new ones need to be replaced. That, in fact, might be the answer. With that expectation in mind, we eliminate everything except (C). Is (C) critical? Yes; we can complete the analysis by cases. If the new designs will go up in price and/or go out of production, the plan will fail. If they don't, the plan may succeed. The correct answer is (C).