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': "Second most common cause of chromosomal abnormality causing mental retardation - \nSelect and explain. \nA. Down's syndrome, B. Fragile X syndrome, C. Edward syndrome, D. Patau syndrome", 'role': 'user'}, {'content': 'Answer: B \nExplanation: "Fragile X syndrome is the second most common genetic cause of mental retardation, after Down syndrome".', 'role': 'assistant'}]