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': 'Which muscle has an indirect effect on the extent of impression in labial vestibule (maxilla) \nSelect and explain. \nA. Orbicularis oris, B. Buccinator, C. Masseter, D. Levator anguli oris', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]