Final answer:
The sparseness of people in Northern Canada is caused by the cold climate and the harsh living conditions, which include brutally cold winters and poor soils unsuitable for agriculture.
Step-by-step explanation:
The sparseness of people in the northern areas of Canada is primarily caused by the cold climate and challenging living conditions. The regions in the North have brutally cold winters, a short growing season, and poor soils, making it difficult for year-round agriculture and large-scale human settlement. Furthermore, the territory north of the tree line, which extends beyond the Arctic Circle, is immense and subject to cold continental and arctic climates. These harsh conditions are why most inhabitants choose to live in the forested areas rather than in the frozen Arctic.
In addition, Northern Canada is mostly unsuitable for permanent human settlement outside of the small communities that have adapted to these conditions. The sparsely populated areas have economies based on forestry and extraction, and it is known for its significant native populations. Most Canadians live close to the US border, where the climate is milder and more conducive to settlement and economic activities.
Thus, the final answer to the question "What causes the sparseness (thinness) of people in the northern areas of Canada?" is C) the cold climate.