US stocks closed mixed Monday as investors kept an eye on upcoming economic negotiations in Washington and Europe. The dollar gained ground against the euro and the pound but lost ground versus the yen. Light sweet crude oil for January delivery fell 54 cents to $87.74 a barrel on the New York Mercantile Exchange. Gold futures lost $1.80 to $1,749.60 an ounce. The Dow Jones industrial average dropped 42.31, or 0.33 percent, to 12,967.37. The broader Standard & Poorâ€™s 500 index fell 2.86, or 0.20 percent, to 1,406.29. The technology-heavy Nasdaq composite index rose 9.93, or 0.33 percent, to 2,976.78.