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: Dental
[{'content': "The term space maintenance refers to \nSelect and explain. \nA. The preservation of a space for a permanent tooth in a child's mouth., B. The preservation of the total arch length or of all the permanent teeth in the arch in a child's mouth, C. The prevention of mesial drift after the Loss of a tooth, D. None of the above", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]