Snapping a four-day rally, the Sensex at the Bombay Stock Exchange declined 100 points, or 0.6 percent, to 17,705, on profit-booking by investors, amid falling Asian and European markets, today. The Sensex had gained over 1,000 points in the past four trading sessions. The Nifty at the National Stock Exchange dropped 34 points, or 0.6 percent, to 5,327. Stock markets in Japan, China, Hong Kong, Singapore and South Korea lost between 0.2 percent and 1.7 percent.