An economist hypothesizes that people will buy less gasoline at $3.00 per gallon than at $2.50 per gallon. In order to test this hypothesis and turn it into a theory, which of the following observations would be most appropriate?

A. People buy more gasoline at $3.00 per gallon
B. People buy less gasoline at $2.50 per gallon
C. People buy less gasoline at $3.00 per gallon
D. People buy more gasoline at $2.50 per gallon