Rising for the fourth straight session, the Sensex at the Bombay Stock Exchange zoomed 727 points, the biggest single-day gain in over 4 years, to end just below the 20,000-mark, at 19,997, today on heavy buying by investors amid strengthening rupee and solid trade data. The Sensex had advanced over 1,000 points in the previous three trading sessions. The Nifty jumped 216 points, to 5,897.Stock markets in Japan, China, Hong Kong, South Korea and Singapore climbed between 1 percent and 1.5 percent.