PT 17 S4 Q18

One way governments can decrease air pollution is to impose a tax on industrial ... ...

Which one of the following circumstances would most seriously undermine the conclusion "Such a tax would induce industry to substitute less-polluting fuels for those carrying a higher tax" (lines 16-19)?
(A) The fuel taxed at the highest rate costs considerably less to buy than fuels taxed at lower rates.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Practice Set: Government & Economics Mix 3