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': 'Broadbent cephalostat uses: \nSelect and explain. \nA. 2 x-ray sources and 2 film holders., B. 1 x-ray source and 1 film holder, C. 1 x-ray source and 2 film holders, D. None of the above.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]