题目选项分析

In the nation of Partoria, large trucks currently have a much higher rate of traffic accidents per mile driven than other vehicles do. However, the very largest trucks—those with three trailers—had less than a third of the accident rate of single- and double-trailer trucks. Clearly, therefore, one way for Partoria to reduce the number of traffic accidents would be to require shippers to increase their use of triple-trailer trucks.

Which of the following, if true, most seriously weakens the argument?

【选项】In Partoria, the safety record of the trucking industry as a whole has improved slightly over the past ten years.