The correct answer is C) money.
After the Persian War, Sparta, Athens, and other Greek communities collected money to ward off future external attacks.
We are talking about ancient Greek times, approximately in the 5th century BC. Persian King Darius commanded one of the most powerful armies of the time but was defeated by the Athenians in the Battle of Marathon in 490 BC. Then, it was Darius' son, who tried to capture Athens but also was defeated. To prevent other invasions, Sparta, Athens, and other Greek communities collected money to ward off future external attacks.
