Lifted by an encouraging GDP growth forecast for this fiscal, the Sensex at the Bombay Stock Exchange closed with a modest gain of 29 points, or 0.2 percent, at 18,037, today, on selective buying by investors, after fag-end profit-booking eroded initial gains. The Nifty at the National Stock Exchange ended flat, at 5,396.Stock markets in Japan, Hong Kong, South Korea and Singapore ended mixed.