In lack luster trading, the Bombay Stock Exchange benchmark Sensex today fell by over 70 points. After moving in a narrow range, the 30-share index dropped 70.31 points to close at 16,740. The wide-based National Stock Exchange index Nifty also lost 26 points to end the day at 4,970. Trading volume declined as investors refrained from enlarging their positions ahead of the Reserve Bank's quarterly monetary policy tomorrow.