The correct answer is B. Chamberlin.
Edward Hastings Chamberlin (1899-1967) was an American economist who is best known for his work on imperfect competition. He developed the theory of monopolistic competition, which is a market structure in which there are many firms selling similar but not identical products. In monopolistic competition, firms have some market power, but they are not able to set prices without considering the prices of other firms.
Chamberlin’s work was published in his 1933 book The Theory of Monopolistic Competition. The book was highly influential and helped to shape the field of industrial organization.
A. Calder is an American lawyer and politician who served as the 38th Attorney General of the United States from 1989 to 1993. He is not known for his work on economics.
C. Samuelson is an American economist who won the Nobel Memorial Prize in Economic Sciences in 1970. He is best known for his work on general equilibrium theory and welfare economics. He is not known for his work on imperfect competition.
D. Mrs. John Robinson is not a well-known economist. There is no record of her having made any significant contributions to the field of economics.