Final answer:
The correct option is B.
The sparse population density in Northern Canada is primarily due to the presence of the tundra biome, which has extremely cold temperatures and limited potential for agriculture or human settlement.
Step-by-step explanation:
The most probable reason for the population density pattern in the areas of Canada furthest from the US/Canada border is B. That area of Canada contains the tundra biome. Northern Canada, which is sparsely populated, includes the tundra biome characterized by extremely cold temperatures, a short growing season, and perma-frost. These conditions severely limit the potential for agriculture, human settlement, and urban development. Most people in Canada live closer to the US border where the climate is more temperate, the soil is more fertile, and the growing seasons are longer, favoring agriculture and urbanization. This understanding is consistent with the physical geography and climate patterns of the region, as well as historical settlement patterns influenced by the proximity to the United States, economic opportunities, and the habitability of the land.