The correct answer is (b). This theory had many early independent originators, including Adam Smith when he wrote in the An Inquiry into the Nature and Causes of the Wealth of Nations that “The value of any commodity, therefore, to the person who possesses it, and who means not to use or consume it, himself, but to exchange it for other commodities, is equal to the quantity of labour which it enables him to purchase or command.” Marx further developed refined this theory: “We see then that that which determines the magnitude of the value of any article is the amount of labour socially necessary, or the labour time socially necessary for its production.”