Identify the compulsion in the following example. demarco can't stop thinking about his book collection, which includes hundreds of first editions. he wants it to be in a particular order. he spends hours every day organizing his books alphabetically by author, then by color, then by size.

a. thinking about the order of the books all the time
b. thinking about the books all the time
c. having hundreds of first editions in his book collection
d. organizing the books

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