The Sensex fell by over 240 points, or 1.37 per cent, in the opening trade on Monday, snapping the four-session winning streak.The 30-share index, which gained nearly 412 points in the past four sessions, fell by 240 points to 17,337 points in the opening trade with all the sectoral indices trading in the negative.The wide-based National Stock Exchange index Nifty dipped by 76 to 5,187 points. Brokers said RBI's decision to raise key short-term lending and borrowing rates by 25 basis points each as part of its policy to tighten money supply to combat inflation, mainly led to the downfall in markets day.