When Amebiasis Is Strongly Indicated but No Parasitic Forms Are

When amebiasis is strongly indicated but no parasitic forms are detected from any of three submitted fecal samples, the next step might be

A) to diagnose based on clinical findings and begin treatment.
B) to collect material obtained from sigmoidoscopy and examine for parasites.
C) to collect another series of three fecal samples and submit for parasitic examination.
D) to collect duodenal drainage and examine for parasites.