THE AVERAGE PRICE OF A GALLON OF REGULAR UNLEADED HAS FALLEN UNDER FOUR DOLLARS, ACCORDING TO THE IOWA DEPARTMENT OF AGRICULTURE’S WEEKLY FUEL PRICE SURVEY.  THE AVERAGE PRICE IS $3.81, DOWN 19 CENTS FROM LAST WEEK.  THE AVERAGE PRICE IS 88 CENTS HIGHER THAN A YEAR AGO.  THE NATIONAL AVERAGE IS $4.16 A GALLON, DOWN 14 CENTS FROM A WEEK AGO.  DIESEL PRICES FELL ANOTHER 12 CENTS TO $4.89 A GALLON, COMPARED TO $3.12 A YEAR AGO.