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': "Heller's syndrome is characterized by regression of milestones after _________ \nSelect and explain. \nA. 1 year, B. 2 years, C. 3 years, D. 6 months", 'role': 'user'}, {'content': "Answer: B \nExplanation: Heller's syndrome (childhood disintegrative disorder) is characterized by normal development till the age of 2 years. After which there\xa0is loss of social, motor & language skills.", 'role': 'assistant'}]