Commodities fell sharply Friday, giving back virtually all of Thursday's gains after an unexpected surge in the dollar triggered risk aversion and profit-taking across financial markets. Oil and corn plunged almost 4% and copper more than 2% as the dollar gained ground against the euro. The Reuters-Jefferies CRB index, a basket of 19 commodities, lost all of the 2% it gained Thursday when the dollar fell steeply after third-quarter economic data