The correct option is
A Endoparasitic flatworms
Tapeworms also known as flatworms belongs to phylum Platyhelminthes. Most adults are endoparasites of vertebrates and are highly adapted to this role. There is usually a primary host and also one or two intermediary hosts which are often an invertebrate. They have no gut and absorb nutrients directly from the digestive tract of the host where they live.
They feed on the cells, cell fragments, tissue fluids or blood of their host. So, the correct answer is option A.