NEW YORK CITY: The nation's unemployment rate improved dramatically in February, falling to 5.5 percent, as the country posted its biggest one-month job increase since 1983. However, the good news sent a surprised Wall Street reeling. The Dow Jones industrial average closed down 171.24 to finish at 5470.45, the third largest net one-day drop ever. Other markets followed suit. The NYSE composite was down 10.31 at 339.83, the Standard & Poor's 500 composite declined 20.46 at 633.19, the AMEX market value index was down 10.25 at 560.06, and the Nasdaq composite was off 23.38 at 1,069.74. The report driving the decline revealed that American businesses added 705,000 jobs in February, and that the national unemployment rate dropped to 5.5 percent from 5.8 percent, another significant improvement. Against the background of such potent economic expansion, the Federal Reserve is unlikely to lower interest rates on when its policy committee meets on March 26th. Lower interest rates would benefit U.S. businesses by reducing the cost for corporations borrowing money and improve earnings.