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': 'Which of the following post is most difficult to bond in the root canal: \nSelect and explain. \nA. Zirconia ceramic post., B. Carbon fiber reinforced post., C. Polyethylene fiber reinforced post., D. Glass fiber reinforced post.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It is because zirconia cannot be etched.', 'role': 'assistant'}]