Identify which of the following sentences has correct subject-verb agreement.
a. A swarm of flies hover over the dumpster behind the barbecue restaurant.
b. The army of ants are trying to invade our picnic!
c. As we watch, a school of brightly colored fish dart to and fro in the aquarium tank.
d. In a basket lined with blankets, a litter of kittens is nursed by its mother.