The correct answer is: "the whole economy".
The two main fields in which the study of economics is divided are macroeconomics and microeconomics.
Macroeconomics studies the behaviour of the economy as a whole. It aims to develop indicators that accurately picture the functioning of the economy of a certain country or region, and to forecast future tendencies.
On the other hand, microeconomics analyses the individual decisions made by the different agents that participate in the economy (for example, households, firms, public sector, etc), the motivations behind their choices, which is the optimal alternative on each scenario, etc.