Stock futures were plunging to start the week's trading as U.S. oil prices topped $100 a barrel amid the U.S.-Iran conflict, raising fears higher energy prices could dramatically slow the U.S. economy. The Dow Jones Industrial Average is coming off its biggest weekly slide in nearly a year. Futures tied to the Dow fell 966 points, or 2%. S&P 500 futures and Nasdaq 100 futures each tumbled 1.6%. West Texas Intermediate crude jumped 18% to above $108 a barrel, its first time above the $100 level