it would be B,
search for letter written by poor laborers during the Great Depression
No idea bro ask yourself that
Your answer would be population density.
The word "unique" means something that is unlike anything else. In urban areas, it's mostly heavily populated due to the amount of residential, business, and suburban areas. Urban areas are packed with houses, apartments, businesses, and etc. When you go into the country side of town, they're not heavily populated due to it being mostly land and not residential places.
