Which of the Following Features Have Not Helped Giardia Become

Which of the following features have not helped Giardia become the most common intestinal parasite?

A) It can be transmitted via fecal- oral route, via contaminated fomites, or from direct contact with an infected patient.
B) It lives in animals other than humans.
C) No drugs are currently available for treatment.
D) Ingesting as few as 10 cysts is sufficient to establish infection.
E) A tough cyst form that resists chlorine disinfection used for municipal water treatment, UV light, and freezing.