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': 'Shape of class 1 preparation of lower first premolar : \nSelect and explain. \nA. Dumbell shape, B. Y shape, C. Butterfly shape, D. No definite shape', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Shapes of class I preparation:', 'role': 'assistant'}]