Answer:
Correct answer is D) Mountains.
Step-by-step explanation:
D is the correct as the mountains presented natural barriers between different city-states. That is why city-states were created in a certain geographical area.
A is not correct as except Peloponnesian peninsula, peninsulas in Greece were not separating city-states.
B is also not correct as most of city-states were created inland.
C is not correct as plains were connecting, not separating the city-states.