Falling for the first time in six days, the Sensex at the Bombay Stock Exchange declined 216 points, or 1.1 percent, to close at 19,782, on investor caution ahead of industrial output and inflation data, and the rupee weakening against the dollar on Thursday.The Sensex had advanced over 1,750 points in the previous five trading sessions. The Nifty at the National Stock Exchange fell 62 points, or 1.1 percent, to 5,851.But stock markets in China, Hong Kong, and Singapore gained between 0.1 percent and 0.6 percent.