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': 'The objective of the access cavity preparation is to gain direct access to \nSelect and explain. \nA. Pulp chamber, B. Canal orifice, C. Apical foramen, D. Middle third of the canal', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]