单选题 Kyle: The rate of highway fatalities per 100 million miles driven was about a third lower last year than ten years ago. The decrease is mainly attributable to greater use of seat belts and to less drinking of alcohol by drivers, but last year's sluggish economy also contributed, by curtailing driving.
Lisa: The economy could not have been a factor, because even if fewer fatalities occur when fewer miles are driven, the number "per 100 million miles driven" is what you were discussing, and that figure would not fall merely because fewer miles were driven.
Lisa's objection is based on