Which of the following is measured by productivity? A. How much gross national product results from inputs of labor. B. The total value of all goods and services produced by a national economy. C. How much output is necessary to produce a certain level of demand. D. The standard of living relative to purchasing power parity. D E. How much a system produces with the resources needed to produce it.

The correct answer is E. Productivity is a measure of how much output is produced with a given set of inputs. It is typically measured as the ratio of output to input, where output can be goods or services produced, and input can be labor, capital, or other resources used in the production process. Option A is incorrect because gross national product (GNP) is a measure of the total value of all goods and services produced by a country's residents, regardless of whether they are located within the country or abroad. It is not a measure of productivity. Option B is incorrect because the total value of all goods and services produced by a national economy is referred to as the gross domestic product (GDP), not productivity. Option C is incorrect because it describes a concept related to production planning and demand forecasting, not productivity. Option D is incorrect because it describes a concept related to purchasing power parity, which is a measure of the relative value of different currencies, not productivity.