Trimming its initial gains, the Sensex at the Bombay Stock Exchange turned almost flat in late morning trade today. The 30-share index, which had opened 80 points in the green, was trading just 24 points up at 31,335, a short while ago.The Nifty at the National Stock Exchange was trading 10 points in the green at 9,668.At the foreign exchange market, the rupee weakened by 10 paise to Rs. 64. 53 against the dollar in opening trade.