Concept:Ectoparasites are organisms that live on the outer surface of the host’s body.Explanation:Tapeworms, liverflukes, and roundworms all live inside the host’s body.These are therefore endoparasites, not ectoparasites.A louse attaches itself to the skin or hair of farm animals.It feeds on the host’s blood or skin debris from the outside.Since it remains on the surface, the louse qualifies as an ectoparasite.Answer:B. louse