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': 'Instrumentation zone in periodontal therapy is: \nSelect and explain. \nA. The portion of the tooth where calculus (or) necrotic cementum is found, B. C.E. Junction, C. Exposed root surfaces, D. Deep periodontal pocket', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]