This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parasitology, Subject name: Microbiology
Giardia lamblia: 
Select and explain. 
A. Is the only flagellate parasite without a cystic stage, B. Infection happens by ingestion of trophozoites in food and water, C. Is the only protozoan parasite found in the lumen of small intestine, D. May sometimes invade the blood stream and cause ectopic lesions
C: Is the only protozoan parasite found in the lumen of small intestine
Answer: C: Is the only protozoan parasite found in the lumen of small intestine 
Explanation: Ans. is 'c' i.e., is the only protozoan parasite found in the lumen of small intestine(Ref: Harrison, 19th/e, p. 1930; 18th/e, p. 1730; D.R. Arora, 3rd/e, p. 44)* Only protozoan found in the small intestine, patient complain of dull epigastric pain, flatulence, and chronic diarrhoea, steatorrhoea, stool is voluminous, foul smelling and contain large amount of mucus, patient loses weight.* Enterotest is employed and ELISA test is developed for the detection of Giardia antigen in faeces.