The correct answer is B, Cryptosporidium parvum.  Cryptosporidium parvum, which is also pathogenic to humans, naturally infects cattle (calves).  Because of its small size and resistance to chlorine, C. parvum pass through water treatment facilities and remain infectious.  C. hominis is another important Cryptosporidium species which is associated with anthroponotic transmission.  To date, Eimeria bovis and Cyclospora papionis are coccidia not associated with human infection.  Isopora belli has not been associated with outbreaks of diarrhea.

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