The Sensex at the Bombay Stock Exchange gained 35 points, or 0.2 percent, to 20,259 in opening trade, this morning, on selective buying by funds and retail investors.But later the Sensex turned volatile, and after swinging between gains and losses, stood 74 points, or 0.4 per cent in positive territory, at 20,298 in afternoon trade, a short while ago.Stock markets China, Indonesia, Hong Kong, Singapore and South Korea had lost between 0.1 percent and 0.7 percent, today. The US Dow Jones Industrial Average ended 0.1 per cent lower in yesterday's trade