Final answer:
The correct answer to the question is A) Beringia, which is the land bridge that connected Siberia and Alaska, facilitating the migration of the first inhabitants to what is now the United States and Canada.
Step-by-step explanation:
The first inhabitants of present-day United States and Canada migrated probably from Asia over Beringia, a land bridge that once connected what are now Siberia and Alaska. Therefore, the correct answer is A) Beringia. During the last ice age, global sea levels were significantly lower, which exposed the land bridge, allowing humans and megafauna to migrate across. These migrations are believed to have taken place between about 20,000 and 14,000 years before present (BP).
As the glaciers melted, rising water submerged Beringia, creating the Bering Strait we know today. These early humans eventually populated the full expanses of North and South America, developing into diverse and complex societies.