Macroeconomics encompasses the study of:

a. a firm's production function.

b. average cost of production.

c. national production.

d. a household's consumption decisions.

The answer is c.

In the narrowest sense, the difference between microeconomics and macroeconomics is that macroeconomics studies the behavior of aggregate variables such as national output, aggregate employment and prices, while microeconomics studies the behavior of individuals and firms. However, this is not to say the two are exclusive of each other. To the contrary, the behaviors of aggregate variables are simply some aggregations of individuals choices. On the flip side, individuals choices are also affected by macroeconomic conditions.