This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Which of the following organism is biggest ? \nSelect and explain. \nA. Balantidium coli, B. Entamoeba coli, C. Escherichia coli, D. Entamoeba histolytica', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Balantidium coli", 'role': 'assistant'}]