Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange plunged 478 points, or 2.7 percent, to 17,446, on Monday, on sustained profit-booking, and as falling global markets, and rising crude oil prices hurt investor sentiment. The 30-share Sensex had lost more than 500 points in the previous three trading sessions. The Nifty at the National Stock Exchange dropped 148 points, or 2.7 percent, to 5,281.Stock markets in Japan, Hong Kong, Singapore and South Korea lost between 0.1 percent and 1.4 percent.