The Sensex at the Bombay Stock Exchange declined 103 points, or 0.5 percent, to again close below the 20,000 mark, at 19,924, on profit-booking by investors, today. The Nifty at the National Stock Exchange fell 35 points, or 0.6 percent, to 6,019.Stock markets in Japan, China, Hong Kong, South Korea and Singapore again ended mixed.