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': 'What should be the diameter of post: \nSelect and explain. \nA. 1/2 of root diameter., B. Same as root diameter., C. 1/3rd of root diameter., D. 1/4th of root diameter.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: At least 1mm dentin should be present circumferentially around post.', 'role': 'assistant'}]