Answer:
B. It has a nucleus
Step-by-step explanation:
All living organisms were classified into a large group called DOMAIN. These organisms were classified into two domains viz EUKARYA and PROKARYA depending on whether or not they possess a nucleus. Organisms in the Eukarya domain called Eukaryotes possess a membrane-bound nucleus that houses their genetic material (DNA) while organisms in Prokarya domain called prokaryotes do not possess a membrane bound nucleus.
Based on this, Giardia organism that is described to be an eukaryotic organism that causes illness in cats, dogs and humans is distinguished from any prokaryote by its possession of a membrane-bound nucleus in the cytoplasm of its cell. Any organism referred to as EUKARYOTIC must possess a NUCLEUS.