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 first step in surveying the cast for RPD is: \nSelect and explain. \nA. Establishment of guiding plane, B. Establishment of undercuts for retention, C. Establishment of tooth contour for esthetics, D. Establishment of interferences for major connector', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]