A parasitic organism is one that benefits from its host, but doesn't benefit the host, in fact, it has negative effects to the host.
In this case, we have 4 examples of worms, and we're supposed to find the parasitic one. And, I think this is something we can do without having to go deep into the subject, because at first sight, we can distinguish a worm, that we all know isn't paricularly good - leeches.
→ Leeches are an example of parasitic annelides that live in high-humidity environments, and live partly from the blood they suck from animals and sometimes humans.
Hope it helped,
BioTeacher101
