The average monthly price of regular gasoline in the United States was recorded for the years 1998-2005. Each year's distribution of average monthly regular gasoline prices is shown in the following box plot. The chart shown has box plots indicating the distribution in gas prices for the years 1998 to 2005. The boxplots for 2000 and 2001 do not move on the vertical axis very much, while 2002 and 2003 have a larger shift. Which two consecutive years saw the least amount of change in monthly gasoline prices? a. 1998-1999 b. 2001-2002 c. 1999-2000 d. 2000-2001