Final answer:
In the middle colonies, European settlers were primarily enticed with the promise of free land, which was a significant aspect of colonial mercantilism and contributed to economic growth and opportunities.
Step-by-step explanation:
In the middle colonies, many European settlers were enticed with the promise of free land. This was a key factor in attracting settlers, as ownership of land was associated with wealth and opportunity, reflecting the mercantilist system where colonies were significant for providing raw materials to fuel industrial growth. Economic activities such as the fur trade, lumber and grain production, and livestock were prevalent. Most farmers owned their land, especially in Pennsylvania, and even leaseholds in New York were nearly as profitable as freeholds, due to comparable sizes and output. Therefore, the correct answer is B. free land.