Answer :
The correct answer to this question would be alternative D) They surprised the Persians by crossing the Aegean Sea to attack."
In order to defend themselves from the Persians, the Greeks used naval strategies to surprise the Persians at Sea, where their numbers didn't matter so much. The Persians had far greater numbers than the Greeks.
The Greeks successfully surprised them, and were able to defend their land, by defeating the Persians at sea.