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': 'Prolonged retention is usually needed in \nSelect and explain. \nA. Diastema, B. Mild crowding, C. Anterior cross bite, D. Deep bite', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]