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': 'Most retentive post among the following: \nSelect and explain. \nA. Smooth tapered, B. Serrated tapered, C. Smooth parallel, D. Serrated parallel', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Parallel-sided posts may distribute stress more evenly than tapered posts, which may have a wedging effect.\nSerrated are more retentive than smoother surface.', 'role': 'assistant'}]