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': 'Cholera vaccine effectiveness is - \nSelect and explain. \nA. 20% for 12 months, B. 50% for 12 months, C. 20% for 36 months, D. 50% for 36 months', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 50% for 12 months", 'role': 'assistant'}]