Question

Anna is working on finding the patterns of demographic variation within North America’s populations. What is Anna working on?

population structure
population size
population density
population growth

Answer 1

Population structure: Population structures are the patterns of demographic variation, as in (statistics related to structure of population) within populations.

so your answer would be population structure

found answer in my bio book

Answer 2

I believe that what Anna is working on, given that she wants to find the patterns of demographic variation, is population structure.
This structure deals with variations in age, gender, and other qualities of a population, and I believe that is what she wants to find out.