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
[{'content': 'A 4-year-old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility without RBCs and pus cells. The etiological agent is: \nSelect and explain. \nA. Entamoeba histolytica, B. Giardia lamblia, C. Trichomonas tenax, D. Balantidium coli', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Giardia lamblia(Ref: D.R. Arora, p. 43)* Mature cyst is the infective form of the parasite acquires infection by contaminated water and food. Infection may be acquired by anal oral sexual practices among male homosexuals.* Within 30 minutes of ingestion excystation occurs in the duodenum, cyst hatches out two trophozoites which multiplies and colonize in duodenum and upper part of jejunum.* In acute Giardiasis trophozoite show the typical 'falling-leaf' motility in wet mount examination of faeces.", 'role': 'assistant'}]