With the of people from fertile areas, knowledge of agriculture spread by

Since there are no choices available I would assume that this is the answer. With the settlement of people from fertile areas, knowledge of agriculture spread by constant migration. During the early days, people thrived in their community when there is fertile soil available for all forms of agriculture. But once the land had been used up, people start to migrate to different locations where they can possibly get their new food sources, thus knowledge of agriculture spread into different areas. 

By how to move the wires