The government has spent heavily to clean groundwater contaminated by toxic chemical spills. Yet not even one spill site has been completely cleaned, and industrial accidents are spilling more toxic chemicals annually than are being cleaned up. More of the government' s budget should be redirected to preventing spills. Since prevention is far more effective than cleanup, it makes little sense that the entire annual budget for prevention is less than the amount spent annually on one typical cleanup site. The proposal about how the government's budget should be redirected plays which one of the following roles in the argument? ['It presents an objection to another proposal mentioned in the argument.', 'It is a presupposition on which the argument is explicitly based.', 'It is the claim that the argument as a whole is structured to support.', 'It represents an unsupported speculation.']