Pure science—research with no immediate commercial or technological application—is a public good.
Conclusion
Society’s that want to reap benefits of pure science should use public funds to support pure science research.
Evidence (since)
Pure science is a public good and requires lots of money, but doesn’t provide profits in the short term. Private corporations aren’t going to back science that doesn’t provide profits in the short term.
Evaluation
Because the claim they’re asking about is prefaced by Since, we know that it functions as support for the other half of that sentence. The other half of the sentence is the author’s main conclusion. So we’d call this a premise in support of the main conclusion.
Goal
Look for evidence / support / premise for the conclusion that is the final claim of the paragraph.