U.S. stocks slumped on Friday, putting the S&P 500 on track for its third straight weekly decline, as a robust dollar threatened to erode the profits of multinationals and tumbling crude oil prices pressured energy shares. NEW YORK: U.S. stocks slumped on Friday, putting the S&P 500 on track for its third straight weekly decline, as a robust dollar threatened to erode the profits of multinationals and tumbling crude oil prices pressured energy shares.