Humans infected with some types of parasitic worms develop a condition called elephantiasis, which is characterized by swelling of the limbs. Which of the following would be the most likely cause of elephantiasis?

a. The infected human's immune system is fighting the worms.
b. The worm infection is causing a decrease in cardiac output.
c. The worms are blocking the lymph vessels.
d. More blood is flowing through precapillary sphincters.