In another dismal day at the stock markets, the Sensex at the Bombay Stock Exchange dropped 261 points, or 1.5 percent, to close below the crucial 18,000 mark, at 17,776, today. The Sensex fell on continued concerns that inflation will trigger further interest rate hikes and trim corporate earnings. The Nifty at the National Stock Exchange declined 83 points, or 1.6 percent, to 5,313.