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': 'Clinical feature of mouth breathing is: \nSelect and explain. \nA. Pigeon face appearance, B. Proclined mandibular anteriors, C. Shallow and flat maxillary arch, D. Retroclined maxillary anteriors', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]