Original sentence: Resource categories in economics distinguish among such factors of production as:.The distinctions above were first developed in classical economics, including the work of Adam Smith (1776), David Ricardo (1817), and the later contributions of Karl Marx and John Stuart Mill as part of one of the first coherent theories of production and distribution in political economy
Edited sentence: Classical economists distinguished three factors of production:.The distinction above was developed in classical economics, including the work of Adam Smith (1776), David Ricardo (1817), and the later contributions of Karl Marx and John Stuart Mill as part of one of the first coherent theories of production and distribution in political economy