Concept:Comparative cost advantage explains how countries gain by specialising in goods they produce at a lower opportunity cost than others.Explanation:This theory was developed by the classical economist David Ricardo in 1817.It improves on absolute advantage by introducing opportunity cost as the basis for specialisation.A country should produce and export goods it can make at a relatively lower cost, even if it is less efficient overall.Adam Smith, Thomas Malthus, and Irving Fisher are associated with other economic ideas, not this theory.Answer:D. David Ricardo