According to Oppenheim, international treaties are agreements, of a contractual character, between states or organizations of states, creating legal rights and obligations between the parties (Oppenheim, vol. I, 1992). The Vienna Convention defines treaty as “an international agreement concluded between states in written form and governed by international law” (Art. 2(1)/a). Thus, every treaty is an agreement, but not all agreements are treaties. The correct answer is E.