Final answer:
The Greeks' major advantage in the Greco-Persian Wars was their strong naval forces, particularly the Athenians' focus on building a significant fleet of triremes. so, option a is the correct answer.
Step-by-step explanation:
The major advantage the Greeks had in both Greco-Persian Wars was strong naval forces. Particularly during the second invasion by the Persians in 480 BCE, the Athenians, led by Themistocles, had heavily invested in a powerful navy, building hundreds of warships known as triremes. This strategic focus on naval capacity allowed the Greeks, especially the Athenians, to challenge and ultimately overcome the significantly larger Persian navy. Despite the vast numbers of the Persian army, their core strength was in their cavalry, whereas the Greek success was derived from the effectiveness of their naval strategy and the unity and fighting prowess of their sailors and soldiers.
The major advantage that the Greeks had in both Greco-Persian Wars was their strong naval forces. The Athenians, in particular, built a powerful navy consisting of hundreds of warships called triremes. This naval strength allowed the Greeks to effectively combat the Persian navy and protect their own territories. It was a significant factor in the Greeks' victories in both wars.