What is the first phase of urbanization, as experienced in the united states?

What is the first phase of urbanization, as experienced in the United States? The first phase of urbanization is migration to large coastal cities. The second phase of urbanization is migration from coastal cities to suburbs and smaller cities. The third phase of urbanization is migration for the North and East to South and West. Through urbanization environmental problems typically decline due to the spread of people over a larger space rather than a lot of people in a small space. 

The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.