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': 'Mandibular ridge resorption causes \nSelect and explain. \nA. Widening of posterior ridge, B. Widening of anterior ridge, C. Narrowing of posterior ridge, D. Widening of maxillary residual ridge', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]