Explanation:

- Option 1: Nationals

Refers to the citizens of a country, irrespective of where they reside. National income typically doesn't consider only nationals.

- Option 2: Economic territory

Involves the geographic area under a government’s jurisdiction. National income is not limited to this territory.

- Option 3: Residents

National income includes the incomes of all residents, meaning those who have their primary economic interest within the territory.

- Option 4: Both residents and non-residents

Non-residents aren't usually the primary focus for calculating national income since it centers on those residing within the country.

In essence, national income is about the income of residents, supporting economic activities within the nation.