I believe the answer is all of the above
<span>the answer is social class hierarchy
What distinguishes a civilization from a simple group of people is the separation of works/job (specialization of labors) that humans do so every needs of all members in that civilizations is fulfilled.
During this separation, some people will hold more so-called 'important' jobs compared to others (such as kings, business leaders, high-priests, etc) and will naturally formed a social hierarchy among them.</span>
Now,
Since the "x" and the "4" have the same exponent and they equal eachother,
x = 4
During the industrial revolution, more people were needed in factories than in farms. This migration from farms to cities was known as the business revolution.
