Law-making treaties set the rules of international law in each field. The Vienna Convention of Law of Treaties, the Law of the Sea Convention, Geneva Conventions and human right conventions are the examples of this category.

Treaty  contracts deal with a narrow area of  practice between states and they resemble contracts in national legal systems. Trade agreements between states can be given as an example; when a state supplies certain goods and the other party pays a sum of money, the obligations of parties under this state contract come to an end.

As also understood from the information given, the correct answer is D. Trade agreements between states is an example can be given for treaty contracts.