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: Pediatrics
[{'content': "Which is MC genetic cause of mental retardation – \nSelect and explain. \nA. Tuberous sclerosis, B. Cri–du–chat syndrome, C. Fragile–x–syndrome, D. Angel's syndrome", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]