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: Social & Preventive Medicine
[{'content': 'Mental retardation is defined if IQ is below – \nSelect and explain. \nA. 90, B. 80, C. 70, D. 60', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]