1. emigration leaving one's homeland to settle in a new place 2. immigration birth rate insufficient to replace the existing population 3. migration resources being used up at a faster rate than they can be replenished 4. overpopulation the movement from one place to another 5. sustainable development the increase in the population of a city 6. underpopulation the number of people exceeds the available natural resources in an area 7. unsustainable development the ability to meet current needs without reducing the ability to meet future needs 8. urbanization the movement of people to a new country

I believe that what you need is to match the word with the definition. Here it is!:

emigration
leaving one's homeland to settle in a new place

immigration
movement of people to a new country

migration
the movement from one place to another

underpopulation
 birth rate insufficient to replace the existing population

urbanization
development the increase in the population of a city

sustainable
development the ability to meet current needs without reducing the ability to meet future needs

unsustainable development
resources being used up at a faster rate than they can be replenished

 overpopulation 
 the number of people exceeds the available natural resources in an area

Answer light in color; silica-rich;