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': 'A helix is placed for: \nSelect and explain. \nA. Activation, B. Increasing the flexibility and range, C. Esthetics, D. Retention', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]