Rising for the third straight session, the Sensex at the Bombay Stock Exchange gained 93 points, or 0.5 percent, to 17,236, amid firm regional markets, even as the Reserve Bank kept its key policy rates unchanged, today. The Sensex had gained over 500 points in the previous two trading sessions. The Nifty at the National Stock Exchange added 29 points, or 0.6 percent, to 5,229.Stock markets in Japan, Hong Kong, Singapore and South Korea rose between 0.1 percent and 2 percent