Another day of big losses knocked U.S. stocks to their lowest levels in more than a year Monday. Investors dumped high-growth technology and retail companies as well as steadier, high-dividend companies. Oil fell below $50 a barrel for the first time since October 2017. Hospitals and health insurers slumped after a federal judge in Texas ruled that the 2010 Affordable Care Act is unconstitutional. Other stocks wobbled in morning trading, then plunged in the afternoon.