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': 'The most common cause of failure of the seal in the posterior palatal area is: \nSelect and explain. \nA. Under extended distal denture border., B. Overextended distal denture border., C. Distolateral border extended beyond the hamular notch., D. All of the above.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]