Correct answer is a) city-states, medieval states, nation-states.
Explanation:
First city-states emerged on the soil of Mesopotamia. Those were Sumerian city-states. Medieval states emerged after the fall off Roman Empire and nation-states were created afterwards. Most of them were created after Revolutions in 18th and 19th Century. That is why A is correct.
B is not correct because this was a development in newer period.
C and D is not correct because city-states emerged before nation-states and medieval states.
