Snapping a four-session winning streak, the Sensex at the Bombay Stock Exchange dropped 33 points, or 0.2 percent, to 17,224, on profit-booking by investors, amid weak Asian markets, today.The Sensex had gained 620 points in last four trading sessions. The Nifty at the National Stock Exchange fell 13 points, or 0.2 percent, to 5,228.Stock markets in China, Hong Kong, Singapore and South Korea lost about 0.6 percent, each.