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': 'Indirect retainers of a partial denture: \nSelect and explain. \nA. Engages undercut areas, B. Most effective when close to direct retainers, C. Must be constructed with flexible materials like plastics, D. Should resist rotatory forces about a fulcrum', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]