The correct answer is D. Robbins.
A. C. Pigou was a British economist who is best known for his work on welfare economics. He defined economics as “the study of wealth and its production and distribution.”
Alfred Marshall was a British economist who is considered one of the founders of neoclassical economics. He defined economics as “the study of mankind in the ordinary business of life.”
J. B. Say was a French economist who is best known for his law of markets, which states that “supply creates its own demand.” He defined economics as “the science of production, distribution, and consumption of wealth.”
Lionel Robbins was a British economist who is best known for his definition of economics as “the science which studies human behavior as a relationship between ends and scarce means which have alternative uses.”
Robbins’ definition of economics is the most widely accepted definition today. It emphasizes the scarcity of resources and the need to make choices among alternative uses.