Suppose an economist collects the following data between May and December of a given year: gasoline prices rose sharply, consumer incomes remained constant, consumers purchased more fuel efficient vehicles than in the previous year, the size of the population did not change, sales of gasoline decreased by 15 percent. Which of the following theories could be tested with this information? a. When consumer incomes rise, gasoline purchases rise.
b. No economic theory could be tested with this information.
c. When the population increases, purchases of fuel efficient vehicles increase.
d. When the price of gasoline rises, gasoline purchases fall.