Since the mayor's publicity campaign for Greenville's bus service began six months ago, morning automobile traffic into the midtown area of the city has decreased seven percent. During the same period, there has been an equivalent rise in the number of persons riding buses into the midtown area. Obviously, the mayor's publicity campaign has convinced many people to leave their cars at home and ride the bus to work.
Which of the following, if true, casts the most serious doubt on the conclusion drawn above?
Fares for all bus routes in Greenville have risen an average of five percent during the past six months
The mayor of Greenville rides the bus to City Hall in the city's midtown area
Road reconstruction has greatly reduced the number of lanes available to commuters in major streets leading to the midtown area during the past six months
The number of buses entering the midtown area of Greenville during the morning hours is exactly the same now as it was one year ago
Surveys show that longtime bus riders are no more satisfied with the Greenville bus service than they were before the mayor's publicity campaign began
剩选项c和e,选项e讲的survey sample是以前就坐bus的人,他们对bus service有没有态度都不能影响mayor campaign,应该是以前不take bus的人,现在take 了bus才是变量
选项c就是new premise to attack argument
因果推理 因为 一个升一个降 所以 是运动起的效果