Which of the following is the best example of a scarce factor of production? (A) Money (B) Food (C) Air (D) Airplanes (E) Established knowledge

To determine the best example of a scarce factor of production, let's analyze each option: (A) **Money**: While money can be scarce, it is not a factor of production itself. It is a medium of exchange used to facilitate the purchase of factors of production. (B) **Food**: Food is a product of the factors of production (land, labor, capital, and entrepreneurship) and can be scarce, but it is not a factor of production. (C) **Air**: Air is generally considered abundant and is not scarce in most contexts, so it does not qualify as a scarce factor of production. (D) **Airplanes**: Airplanes are a product that requires various factors of production to create. They can be scarce in certain contexts, but they are not a fundamental factor of production. (E) **Established knowledge**: Established knowledge can be considered a scarce factor of production because it represents the expertise and skills that are not universally available and are essential for production processes. Based on this analysis, the best example of a scarce factor of production is: **(E) Established knowledge**.