Final answer:
The arrival of Christopher Columbus opened the Americas to European settlement.
Step-by-step explanation:
The correct answer to the question 'What opened the Americas to European settlement?' is D. The arrival of Christopher Columbus.
Christopher Columbus's arrival in the Americas in 1492 marked the beginning of European settlement in the region. His voyages paved the way for further exploration and colonization by other European powers, including Spain, Portugal, England, and the Netherlands.
Christopher Columbus's arrival in the Americas was a significant event in history as it led to the widespread colonization of the region by European powers, resulting in far-reaching societal, economic, and cultural consequences.