What were the main labor sources in the middle colonies?
family and slaves
immigrants and slaves
immigrants and indentured servants
indentured servants and family

The main labor sources in the Middle Colonies were immigrants and slaves.

Explanation:

First, of all, labor was short in the middle colonies. So they had difficulty to fin workers. That's why they found benefits in slavery and in Immigration, generally from British and German teenagers who signed contracts along with an ocean ticket to start a life in the New World.

The middle colonies were among the colonies that bought more slaves, because of the hard work at the lumber camps, the shipyards, papermaking industry, and sawmill industry.

Another very important population of workers was the Scottish-Irish one. Which were the ones that fought against Native Americans the most. French, Dutch and Scandinavian populations also joined these groups.

d) post-world war i