The correct answer is (d). Duguit was a French jurist who is considered one of the founders of sociological jurisprudence. He argued that law is not a command of the state, but rather a product of social forces. This view is in contrast to the dualist theory, which holds that law is a separate and distinct system from morality.
Triepel, Anzilloti, and Oppenheim were all proponents of the dualist theory. Triepel argued that international law and domestic law are two distinct legal systems, each with its own sources, subjects, and sanctions. Anzilloti similarly argued that international law is a system of law that is separate from and superior to domestic law. Oppenheim also held that international law is a separate legal system, but he argued that it is not superior to domestic law.
Duguit’s view of law is in contrast to the dualist theory in that he does not believe that law is a separate system from morality. He argues that law is a product of social forces, and that it is therefore subject to the same moral standards as any other social institution. This view has been influential in the development of sociological jurisprudence, which is a school of thought that emphasizes the social context of law.