Posting its biggest single day fall in nearly nine months, the Sensex at the Bombay Stock Exchange plunged 317 points, or 1.6 percent, to close at the year's lowest level of 19,325. The Nifty at the National Stock Exchange dropped 91 points, or 1.5 percent, to 5,852.The global markets also fell, on concerns that the US central bank may reduce global liquidity. So the bourses in Japan, China, Hong Kong, South Korea and Singapore dropped between 0.4 percent and 3 percent. The European markets also took a big beating.