Final answer:
Athens and Sparta were both Greek city-states, or poleis, despite their different government systems, with Athens being a democracy and Sparta an oligarchy.
Step-by-step explanation:
Athens and Sparta were both significant city-states in ancient Greece that emerged during the Archaic period and became dominant in the Classical period, but they differed greatly in their government and culture. Athens is known as the birthplace of democracy, marked by its system of direct democracy where adult male citizens had the right to vote on legislation and executive bills. Sparta, on the contrary, was an oligarchy led by two kings and a small group of elites. Despite their differences, they shared one key similarity: both were a polis.
Therefore, the correct answer to the question, which of the following did Athens and Sparta have in common, is A) They were both a polis.