In the nation of Partoria, large trucks currently account for 6 percent of miles driven on Partoria' s roads but are involved in 12 percent of all highway fatalities. The very largest trucks-those with three trailers-had less than a third of the accident rate of single- and double-trailer trucks. Clearly, ttherefore, one way for Partoria to reduce highway deaths would be to require shippers to increase their use of triple-trailer trucks. Which of the following, if true, most seriously weakens the argument? ['So far only the best, most experienced drivers for Partorian trucking companies have been driving triple-trailer trucks.', 'Very few fatal collisions involving trucks in Partoria are collisions between two trucks.', 'In Partoria, the maximum legal payload of a triple-trailer truck is less than three times the maximum legal payload of the largest of the single-trailer trucks.', 'In Partoria, the safety record of the trucking industry as a whole has improved slightly over the past ten years.']