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': 'Resistance form of cavity preparation is: \nSelect and explain. \nA. Flat pulp floor, B. enough depth of the cavity, C. Restricted size of the external walls, D. all of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]