Climbing for the second straight session, the Sensex at the Bombay Stock Exchange gained 133 points, or 0.7 percent, to 20,389, on Thursday, as investors bought stocks with strong fundamentals. The Nifty at the National Stock Exchange rose 42 points, or 0.7 percent, to 6,102.Stock markets in China, Hong Kong, South Korea and Singapore posted modest gains of between 0.1 percent and 0.4 percent.