Arrange the following classifications of countries based on economic productivity from highest to lowest income level: A. Upper-middle-income countries B. High-income countries C. Low-income countries D. Lower-middle-income countries

When we talk about the economic productivity of countries, we classify them based on their income levels. High-income countries are at the top because they have the highest economic productivity and wealth, like the United States or Germany. Next are upper-middle-income countries, which are doing well but not as wealthy as the high-income ones, such as Brazil or China. Following them are lower-middle-income countries, like India or Nigeria, which have moderate economic growth. Finally, we have low-income countries, which struggle the most economically, such as Afghanistan or Haiti.