Question

low population density
limited access to healthcare
high population concentrations

Explanation:

In the context of issues like disease spread or resource distribution, high population concentrations (e.g., in cities) are associated with faster spread of diseases, more demand on resources, etc. Low population density and limited access to healthcare are more about sparse areas or lack of medical resources, while high population concentrations relate to areas with many people in a small space, which is a key factor in various societal and health - related issues.

Answer:

high population concentrations