This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Social and Language Milestones, Subject name: Pediatrics
[{'content': 'Child knows his/her sex at the age of: \nSelect and explain. \nA. 1 year, B. 3 years, C. 5 years, D. 7 years', 'role': 'user'}, {'content': 'Answer: B \nExplanation: A child knows her full name and gender by the age of 3 years.', 'role': 'assistant'}]