Answer: B) The Amish are willing to isolate themselves.
Amish live in their own separate community from other cities or towns. That's how they're able to preserve their culture. I wouldn't say they are far from other Americans since that would imply that there is hundreds of miles of buffer space; but at the same time I would still consider them isolated.
External migration takes place for educational or economic reasons as well, but often, it is politically motivated. An international migrant is someone who moves to a different country. Simply, internal migration refers to the movement of people within a country.