la respuesta es
QUE EL trato entra dos participantes ( pais } con de acuerdos de los convenios internacionales se puede ser de muchas clases: de tipo económico, político, social, cultural, militar, etc
entonses la respuesta puede ser A , B, C , D
As I am thinking you mean "Producers" when you say "Sellers" I am going to go with, Yes. You are correct it is Supply.
(Also the other one is called Demand not price)
Constantine, was the person who found the Byzantine and Constantine was the name of the last Byzantine leader