NEW YORK (AP) — It was a scary good year for investors. It was scary because the U. S. stock market plunged to several historic drops on worries about everything from President Donald Trump’s tariffs to interest rates to a possible bubble in artificial-intelligence technology. In the end, though, it was a great year for anyone with the stomach to stick through the swings. S&P 500 index funds, which sit at the heart of many savers’ 401(k) accounts, returned more than 18% in 2025 through a...