请教xdf讲义上一道题

the country of M has severe air pollution, 80%of which is caused by the exhaust fumes of cars .In order to reduce the number of cars on the road, the government is raising taxes on the cost of buying and running a car by 20%.this tax increase, therefore will significantly reduce air pollution in country M/

which of the following ,if true, most seriously weakens the argument above?

(a)    the government of M is in the process of building a significant number of roadways.

(b)    M is an oil-producing country and is able to refine an amount of gasoline sufficient for the needs of its pollution

(c)    M has had an excellent public transportation system for many years.

(d)    90% of the population of M is very prosperous and has a substantial amount of disposable income

(e)    In M ,cars that emit relatively low levels of pollutions cost 10%less to operate, on the average, than do cars that emit high level of pollutions.

为什么要选e呢?请大家指教.