Concept:National income measures the total monetary value of final goods and services produced in an economy over a period of time, which reflects the country's economic progress.
Explanation:National income is usually measured in terms of Gross Domestic Product or Gross National Product.
It includes the value of all output produced within the country in a given year.
When national income rises over time, the economy is producing more goods and services.
This continuous increase is what economists identify as economic growth.
National income does not directly measure population size, human development level, or the flow of imports into the country.
Hence, national income is used as an indicator to assess a country's economic growth.
Answer:B. a country's economic growth