Option 1 -> Incomplete, excludes the firms/business sector.
Option 2 -> Incomplete, excludes the household sector.
Option 3 -> Includes all three fundamental sectors of domestic economy.
Option 4 -> Trade is not a separate major sector but an activity between sectors.
Hence, Option 3: Firms, government and household sector -> In economic theory, the domestic economy is typically divided into three major sectors: (1) Firms/Business Sector - produces goods and services, (2) Household Sector - provides factors of production and consumes goods/services, and (3) Government Sector - provides public goods, regulation, and policy. These three sectors interact through circular flow of income. While trade exists, it represents interaction with the external/foreign sector rather than being a major domestic sector itself. -> correct