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': 'Passive retention in removable partial dentures is provided by: \nSelect and explain. \nA. Direct retainers, B. Indirect retainers, C. Undercuts, D. Guiding planes', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]