Answer:
D. a booming system of trade
Explanation:
The sea (the Aegean and the whole Mediterranean) became the best means to put the Greek polis in contact with each other and with other civilizations, establishing an active trade of all kinds of products at long distances (reaching North Europe and Central Asia), to the point that many of the city-states depended heavily on maritime trade. The Greeks became excellent sailors, an ability used in civil as well as military affairs.
