Concept:Macroeconomics studies the economy as a whole using aggregates, not individual units.
It treats economic agents as broad groups rather than single persons or single businesses.
Explanation:The main aggregate units in macroeconomics are households, firms, government, and the external sector.
It examines totals such as national income, total investment, total employment, aggregate consumption, and the general price level.
Option A is the correct choice because it lists these units in an aggregative manner: household, firms, government, corporate sector, and external sector.
Options B, C, and D contain individual consumers, individual firms, or only the manufacturing sector, which are microeconomic units rather than macroeconomic aggregates.
Therefore, the correct answer is A.
Answer:A. household, firms, government, corporate sector and external sector