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': 'Lactose nonfermenting are all except - \nSelect and explain. \nA. Shigella sonnei, B. Shigella dysenteriae, C. Shigella flexneri, D. Shigella boydii', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Shigella sonnei * Lactose and sucrose are not fermented except by Sh. Sonnei which ferment them late.", 'role': 'assistant'}]