Answer:
Option D, roundworms
Step-by-step explanation:
Elephantiasis is a disease which caused by round worm known as filarial worm. These worms are spread through a vector agent i.e a female mosquito. A parasite growing with in the worm causes this disease which leads to extreme swelling in the arms and legs. It is transmitted from one human to other through mosquito bites. The worm lives in lymphatic system of humans from which it gets nourishment.
Hence, option D is correct.