The correct answer is C. Revenue.
Revenue is the income that a government receives from taxes, fees, and other sources. It is used to fund government programs and services, such as education, healthcare, and infrastructure.
National income is the total income earned by all residents of a country in a given year. It is calculated by adding up the incomes of all individuals, businesses, and governments.
Gross Domestic Product (GDP) is the total market value of all final goods and services produced in a country in a given year. It is a measure of the size of the economy and is often used to compare the economic performance of different countries.
Economic system is the set of institutions and policies that govern the production, distribution, and consumption of goods and services in a country. There are four main types of economic systems: capitalism, socialism, communism, and mixed economy.
In conclusion, the subject which is related to the income and expenditure of the government is called revenue.