A parasite is a living organism that lives inside or outside of another organism called a HOST in order to obtain nourishment from such organism. A parasite that lives inside its host is called ENDOPARASITE while a parasite that lives outside its host is called ECTOPARASITE.
In this question, a worm that lives inside a bear is a PARASITE because it is living inside the bear, which is the host in order to obtain nourishments. Note that, the answer is not option D because the bear is a HOST not a parasite.
