(D)
GDP is an important concept regarding the wealth produced by the economic activities of a given country. It is an economic indicator that corresponds to all the final goods and services produced by an economy in a certain period of time.
GDP is the economic indicator most used to measure the wealth of a nation and also serves as a benchmark for measuring public investments. For example, it is usually said that a country invests a percental value of GDP in education, health, or that it spends so much of GDP with the judiciary.