LONDON (Reuters) - Crude oil fell sharply on Monday, with U.S. crude briefly dropping below $20 and Brent hitting its lowest level in 18 years, on heightened fears that the global coronavirus shutdown could last months and demand for fuel could evaporate further.Brent crude , the international benchmark for oil prices, was down $1.93, or %7.7, at $23.00 by 0820 GMT, after earlier dropping to $22.76, the lowest since November 2002. U.S. West Texas Intermediate (WTI) crude fell $1.14, or %5.3, to..