The correct answer is: D. None of the above
Microeconomics is the study of the behavior of individual economic agents and how they interact with each other in markets. It is concerned with the choices that individuals make, such as how much to consume, how much to save, and how much to work. Microeconomics also studies the behavior of firms, such as how much to produce, how much to charge for their products, and how many workers to hire.
Macroeconomics is the study of the economy as a whole. It is concerned with the size of the economy, the level of employment, and the rate of inflation. Macroeconomics also studies the causes of economic fluctuations, such as recessions and booms.
The size of national output is a macroeconomic concept. It is the total value of all the goods and services produced in a country in a given year. The level of employment is also a macroeconomic concept. It is the percentage of the population that is working. Changes in the general level of prices is also a macroeconomic concept. It is the rate at which prices for goods and services are rising.
Therefore, none of the above options are microeconomic concepts.