Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange dropped 112 points, or 0.7 percent, to a 28-month closing low of 15,379 on Monday, on persisting concerns about a slowdown in growth, a weakening rupee, and sliding Asian markets. The Nifty at the National Stock Exchange declined 39 points, or 0.8 percent, to 4,613.Stock markets in Japan , China , Hong Kong , South Korea and Singapore fell between 0.3 percent and 3.4 percent, on continuing worries about the euro-zone debt crisis.