Because it is difficult for economists to use experiments to generate data, they generally must a. use whatever data the world gives them. b. substitute assumptions for data when data are unavailable. c. do without data. d. rely upon hypothetical data that were previously concocted by other economists.

a.

Explanation:

Because it is difficult for economists to use experiments to generate data, they generally must use whatever data the world gives them. Economists do not have the luxury of making correct controlled experiments because an economy has many moving parts (variables) which are nearly impossible to replicate. Therefore the best way to study new theories is to use historical data gathered from real world economies.