How do u know if its a and c

The persians landed in the plains near athens. as their army greatly outnumbered that of the greeks, the greeks hoped to find aid from nearby sparta. a long-distance runner named pheidippides was sent from athens to sparta to request , but the spartans were not able to send more soldiers at the time. regardless, the greeks were still able to win the battle. centuries later, legend developed that a runner had been sent from the battle to athens after the greek victory. after reaching athens, the runner proclaimed, "we are victorious! " and then fell to the ground and died. this legendary story is the inspiration for the modern long-distance runs that are performed today. this passage refers to the events of which battle during the persian wars? a. battle of thermopylae b. battle of salamis c. battle of plataea d. battle of marathon