A ball is placed on the ground next to a tree at the top of a hill. The distance, in feet, the ball travels away from the tree during the first 6 seconds after it begins rolling down the hill is shown on the graph. At which interval of time is the ball traveling with the greatest average speed? between x = 0 and x = 2 between x = 2 and x = 4 between x = 2 and x = 6 D between x = 4 and x = 6