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': 'Patient has difficulty in swallowing as a CD wearer. The most probable cause is: \nSelect and explain. \nA. Decreased vertical dimension, B. Increased vertical dimension, C. Thickness of flange, D. Decreased retention', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]