Fossil-fuel producers say that it would be prohibitively expensive to reduce levels of carbon dioxide emitted by the use of fossil fuels enough to halt global warming. This claim is probably false. Several years ago, the chemical industry said that finding an economical alternative to the chlorofluorocarbons (CFCs) destroying the ozone layer would be impossible. Yet once the industry was forced, by international agreements, to find substitutes for CFCs, it managed to phase them out completely well before the mandated deadline, in many cases at a profit. Which one of the following, if true, most strengthens the argument? ['There are ways of reducing carbon dioxide emissions that could halt global warming without hurting profits of fossil-fuel producers significantly more than phasing out CFCs hurt those of the chemical industry.', 'The use of CFCs never contributed as greatly to the destruction of the ozone layer as the carbon dioxide emitted by the use of fossil fuels currently contributes to global warming.', 'In some countries, the amount of carbon dioxide emitted by the use of fossil fuels has already been reduced without prohibitive expense, but at some cost in convenience to the users of such fuels.', 'If international agreements forced fossil-fuel producers to find ways to reduce carbon dioxide emissions enough to halt global warming, the fossil-fuel producers could find substitutes for fossil fuels.']