NEW YORK (AP) — Stocks closed slightly lower on Friday in a quiet day of trading as investors returned from the Christmas holiday. The S&P 500 index fell 2.11 points, less than 0.1%, to close at 6,929.94, the Dow Jones Industrial Average fell 20.19 points, also less than 0.1%, to 48,710.97 and the Nasdaq composite fell 20.21 points, or 0.1%, to 23,593.10. Institutional investors are largely closed out of their positions for the year, so trading was extremely light. Trading on the New York Stock Exchange ...