Ethanol

The conclusion of the argument is that by increasing tax incentives and thus getting people using ethanol, we will use less oil and thus decrease dependence on foreign oil. This is based on the fact that cars get better mileage when they use a blend of ethanol and gasoline than they do when they use just gasoline.

This argument is a little funny actually, because I am not sure what the real point is. Is the point that the mileage is better when ethanol is used? or is it that ethanol is a decent substitute for part of the gasoline and so less gasoline is used and therefore less oil, which is used to produce gasoline, is used?

Anyway, even with that possible ambiguity there's a way to get the right answer.

A)It takes 1.5 gallons of oil to produce 1 gallon of ethanol.

This immediately jumps out as the right answer. Supposedly by using ethanol we can use less oil, but look, it takes a more than a gallon of oil to produce a gallon of ethanol. So even if ethanol works well in cars, and if we therefore were to use ethanol for fuel, the truth is that effectively we would still be using a lot of oil, to produce the ethanol.

So I am guessing this is the answer, but I am still going to check the rest. There could be an even better one, especially as this one has a slight vulnerability to it in that maybe cars get such better mileage with ethanol that even though it takes oil to make ethanol one can still reduce use of oil by using ethanol.

B)Electric cars are cheaper to operate than cars running on the ethanol fuel mix.

This is a typical trap answer used in CR questions involving plans. These trap answers often indicate that the plan is not the best plan available. The thing is the question is about whether the plan is the best plan. The question is about why the plan itself wouldn't work. A plan could work fine without being the best plan, and so this answer choice is irrelevant.

C)It costs thousands of dollars to retrofit an automobile to run on the ethanol fuel mix.

This is another typical trap answer, one involving a topic shift. The conclusion we are seeking to weaken is about use of foreign oil. This answer choice is about cost to retrofit cars. There could be a high cost to retrofitting cars and the plan would still reduce use of oil. So this choice does not affect the conclusion.

D)The ethanol/gasoline blend emits more pollution that regular gasoline.

Here we go again. So the plan might not be a good plan, because in achieving its goal the plan delivers negative consequences, but that does not mean that the plan would not succeed in achieving its goal of reducing use of oil.

E)The ethanol/gasoline blend has not been widely adopted in Europe.

Maybe in the real world this could be a red flag that there is some issue with the plan. If others have not adopted a similar plan, maybe there is some reason they haven't. At the same time, in choice A there is an actual reason why the plan likely won't work, while this choice merely gives us a reason to wonder if there is a reason.

So even with the ambiguity of the prompt and the lack of a specific number to tell us what "get's better mileage" means, the answer choice that casts the "most doubt" on the validity of the legislators' conclusion that the plan will work is A.