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': 'Which of the following is a new slow type palatal expander? \nSelect and explain. \nA. NiTi expander, B. Hyrax expander, C. Quad helix, D. Molar rotator', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]