The plants which depend on other plants are called as parasitic plants. Here the plant which gives shelter and food material to the parasite is called as the host plant. Parasitic plants produce special adventitious roots called as parasitic roots or haustoria which penetrate into the roots or shoots of the host plant to absorb food and other required nutrients.
Homologous means different origin but same function. Ginger is the modified underground storage stem while Sweet potato is modified storage root. Both Ginger and sweet potato are different in origin but have same storage function. Hence option D is correct.