Final answer:
The Green Party and the Socialist Party are the most likely to support a healthcare system that lowers the cost of treatment for everyone, as they favor collective healthcare solutions, while the Libertarian Party prefers minimal government intervention.
Step-by-step explanation:
The question, "Which party would likely be in favor of a healthcare system that lowered the costs of treatment for everyone?" touches on the political party's stance on healthcare policy. Of the options given (a) Libertarian Party, (b) Green Party, (c) Socialist Party, and (d) Independent Party, the Green Party and the Socialist Party are most likely to be in favor of a healthcare system designed to lower costs for everyone. Both parties generally support a more collective approach to healthcare, where sharing the costs across the entire population is standard to ensure comprehensive coverage for all citizens. The Libertarian Party, meanwhile, is least likely to support such a system as they advocate for minimal government intervention in personal affairs, including healthcare. The Independent Party is not a single party with a unified stance on healthcare, so their position would depend on the individual politician.