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: Psychiatry
[{'content': 'Mental retardation is diagnosed if. (Intelligence quotient) is less than \nSelect and explain. \nA. 90, B. 80, C. 70, D. 60', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 70', 'role': 'assistant'}]