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': "The most common causative organism for Traveller's diarrhoea is - \nSelect and explain. \nA. E. coli, B. Shigella, C. Norwalk virus, D. Rotavirus", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]