I have narrowed the answer to these to letter.

An excise tax of .50 per gallon is levied on gasoline. Which of the following is most likely to occur?

C. Consumers of gasoline will buy a smaller quanity and pay a higher price.
D. suppliers of gasoline will increase their quantity supplied to offset the taxes paid to the government.

C. looks like the best answer to me. When gas prices were $4.00 a gallon, people drove less and used less gas.