One thing was that Seas were sometimes difficult to navigate which limited communication - D. this was already a factor which limited the possibility of one united Greece emergin because it made it very difficult to talk to these isolated islands that couldbe found through the difficult-to-navigate seas.
Another thing was that C - some city-states were located on isolated islands.
They were engaged in Activism.
The fortified hill being described here is named Acropolis.
Acropolis is one of the most recognizable and important sites in the Greek history and culture. Acropolis means the "highest city" in literal translation and the word itself is used for many other similar sites but only the Acropolis of Athens is known as The Acropolis. The most famous building here is without a doubt Parthenon.
What case are you referring to?