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': 'Legionnaire disease is caused by- \nSelect and explain. \nA. Motile gram positive, B. Motile gram negative, C. Non-motile gram positive, D. Non-motile gram negative', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]