Explanation:

- Income Method: This approach calculates the national income by summing up all incomes earned by individuals and businesses, including wages, rents, interest, and profits.

- Product Method: Also known as the output method, it measures the national income by calculating the total value of all goods and services produced within a country.

- Expenditure Method: This method involves adding up all the expenditures made in an economy, such as consumption, investment, government spending, and net exports.

- All of These: All the above methods (Income, Product, Expenditure) are valid approaches for measuring national income.

Answer: Option 4 - All of these