A because it does not use the word likely meaning that it’s able to be shown on a map and D is just an opinion. It would be A because it can be placed on a map.
The answer is D- a case study.
It's the same meaning of case as is used in police investigations- "they solved the robbery case". It's one study- or investigation- of something that may happen again.
Here is some information I found on Study.com:
“There are generally three types of settlements: compact, semi-compact, and dispersed. Each is based on its population density.”
I hope this serves you well. Good day.
