Step 1: Understand the question.
The question asks for the reason why the Appalachian Mountain region of the USA has a dense population. We need to identify the correct factor influencing this population density.
Step 2: Analyze each option.
- Option (A) uneven physical condition: This is not a reason for a dense population. In fact, uneven physical conditions often discourage settlement in some areas.
- Option (B) inaccessible mountainous region: This would typically hinder population density, as difficult accessibility often limits settlement.
- Option (C) development of iron-ore and coal mines: The presence of important industries like coal and iron-ore mines in the region attracts a large population for work, leading to density.
- Option (D) war-like condition: This is irrelevant to the population density of the Appalachian region.
Step 3: Conclude the correct option.
The correct answer is (C), as the development of iron-ore and coal mines in the region created jobs and attracted a dense population.
Final Answer:
The correct reason is the development of iron-ore and coal mines.