Critical Reasoning

Studies have shown that an automobile that runs on a blend of 85%
ethanol/15% gasoline gets better mileage than an otherwise similar car
equipped with a gasoline engine. Many American legislators have concluded
that an increase in tax incentives for ethanol production would lessen our
dependence on foreign oil. Which of the following, if true, casts the most
doubt upon the validity of the legislators' conclusion?
"¢ It takes 1.5 gallons of oil to produce 1 gallon of ethanol.
"¢ Electric cars are cheaper to operate than cars running on the ethanol fuel
mix.
"¢ It costs thousands of dollars to retrofit an automobile to run on the ethanol
fuel mix.
"¢ The ethanol/gasoline blend emits more pollution that regular gasoline.
"¢ The ethanol/gasoline blend has not been widely adopted in Europe.

OA:A
My problem with this question.
I like A.
But I also like B,C and D.
I do not understand how can we negate choices B,C and D.
E can be negated because it goes tangentially to the argument.
B->If electric cars are cheaper than people who already have electric cars will not convert to ethanol-mix driven cars. Here no demand,hence no supply, hence no affect of government regulations.
C->If it costs so much too much to convert, why would anybody convert, Hence no demand would generate hence no affect of government regulations.
D->If it emits more pollution, then it thretens the environment and hence it would not be a preferred choice to use ethanol mix. Hence no matter what government does, it there is no demand, there is no sale hence no use of providing tax incntives.

In such problems, its becomes so difficult to figure out the best choice, as so many of them are weakening the argument.
Can anybody tell how to nail such problems ?


Thanks so much in advance.