This stimulus presents us with two economic principles: one regarding when a tax is effective (raises revenue and burdens all & only those persons targeted by the tax), and one regarding when a tax is ineffective (does not raise revenue and costs significant amount of money to enforce).
You are asked to select the answer choice that is most textually supported by these principles. Answer choice (C) comports with the second principle stated by the economist: if the gasoline tax does not raise revenue, it is ineffective, since we are told it costs a significant amount of money to enforce.
Answer choice (E) can be eliminated because we are not told anything in the stimulus about those taxes which "do not cost a significant amount of money to enforce" and which "do not raise revenue." The stimulus only tells us about those taxes that *do* cost a significant amount of money to enforce.
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