The market posted its biggest drop of the year Monday. A steep fall in commodity prices led to a widespread sell-off, as worries about the global economy resurfaced. The Dow dropped 265 points, its worst day this year. The first trigger came from China. News that the world’s second-largest economy slowed unexpectedly pummeled oil, copper, and other commodities. In the market, companies that produce oil and mine for metals fared the worst. A slowdown in China, a huge importer of basic materials like copper, would stymie profits. Oil prices hit their lowest level since mid-December, and gold fell below $1,400 an ounce for the first time in two years.