UnitedHealth, Alibaba, Celsius, Coinbase, Block, Dropbox: Stocks to watch today

U.S. stocks changed little in trading Friday morning; the S&P 500 was flat, the Dow Jones Industrial Average dipped 0.5%, and the Nasdaq rose 0.3% shortly after the market opened. Here are stocks to watch today: Alibaba (BABA+4.93%) stock extended its rally for a second consecutive day, climbing 5% …