I have a question on that problem. According to the textbook answer D) is the correct answer. I can agrue against that. The conclusion is that Country B will be able to reduce its dependence on foreign sources of oil because (premises) it recently embarked on a new program and it can produce enough oil and ethanol to meet its current demand.

The explanation states that if gasoline consumption were to increase at a substantially higher rate than oil and ethanol production, then domestic production will no longer meet domestic demand.

This is a hypothetical situation in the future, that is not part of the conclusion. The conlusion doesn't say whether country B reduces its dependance on foreign oil in this moment only or that reduction in dependance will prevail in the future. Why are we going to assume something that the conclusion doesn't state?

D) Would be a better answer if the conclusion explicitely states that the "reduction in dependance" will be a situation that is going to last in the future and it is not only a current temporary event.

Check out the question. It contains the conclusion: "Country B WILL SUCCEED in its plan to reduce dependence on foreign oil". The word "will" implies that this plan is either underway or will be underway and that it has not yet been judged as a success. We can infer that at a later date the plan will be judged as successful or not. Could anything hurt the likelihood of this plan's success? Yes! If consumption is increasing at a higher rate than production then Country B will not be able to succeed in its plan to reduce dependence on foreign oil.

I hope this helps.

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Jamie Nelson
ManhattanGMAT Instructor