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': 'Distal extension RPD is \nSelect and explain. \nA. Both tissue and tooth borne, B. Tooth borne, C. Class III condition, D. Class IV condition', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]