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 proximal retention grooves for anterior 3/4" crown are placed \nSelect and explain. \nA. Parallel to middle and incisal thirds, B. Parallel to long axis of tooth, C. Parallel to middle and cervical thirds, D. Parallel to cervical, middle and incisal thirds', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]