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': 'In endodontic practice, periapical radiographs are very useful in assessing the \nSelect and explain. \nA. Length of the root canal, B. Presence of infection in the pulp, C. Vitality of the pulp, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]