Answer:
a. Law of Nations
Step-by-step explanation:
The law of the nations (on Latin: ius gentium or jus gentium) was the international law and legal code of ancient Rome. It was designed specifically to dictate the legal rules for foreigners in case they were in conflict with Rome, or that their own rules were unknown.
The law was the same for all the nations and it was adopted by all European civilizations at the time.
The idea behind the law of nations was quality for all and following the natural reason. It is the ground basis for modern international law.