Question

The priesthood, a specialized occupation in a person takes charge full-time of a large religious organization, first developed in which type of societies?

Answer 1

I believe the answer is: Agrarian

A society could be said to has a specialized occupation if there is a clear division of labor that differentiate the duty/job description between one citizen and another.
This division of labor was first created by agrarian society when they separate their workforce to handle different parts of farming process.