One result of this family solidarity was that the foreign farmers in our county were the first to become prosperous. After the fathers were out of debt, the daughters married the sons of neighbours–usually of like nationality–and the girls who once worked in Black Hawk kitchens are to-day managing big farms and fine families of their own; their children are better off than the children of the town women they used to serve.

Which theme is best supported by the comparison in this passage?

A. It is best to stay within your own community.
B. America is built on business.
C. Farming builds healthy, productive people.
D. Families are successful when they work together.