题目选项分析

A think-tank in Michigan has announced a controversial new finding. It concludes that efforts to combat high emissions from cars by taxing gasoline and SUVs are misplaced; rather, governments should be providing consumers with tax incentives to purchase large cars and carpooling with their neighbors to work. They estimate that such a plan would reduce national gas emissions by 23% over the next decade.

Which of the following, if true, casts the greatest doubt on the likely effectiveness of this recommendation?

【选项】The number of cars on the nation's major highways has increased steadily in all major urban centres.