In terms of migration, which of the following is an example of a pull factor?

Pull factors can be better climate, food, resources, jobs 

Afine-grained igneous rock forms as a result of slow cooling.

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.