U.S. stocks edged lower in Friday morning trading, a day after big gains pushed the Nasdaq composite to a record high. Investors were keeping an eye on events in China, where the main stock market plunged, and Europe, where talks between Greece and its creditors remain unresolved with a big debt repayment looming. Among individual stocks, CarMax slumped after reporting disappointing sales figures. CarMax fell 3.7 percent after the used car dealership chain reported fiscal first quarter sales that fell short of forecasts. In China, the main stock index plunged, raising concerns that a bubble in the market may have burst. The yield on the 10-year Treasury note, which falls when prices rise, dropped to 2.2 percent from 2.32 percent late Thursday.