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: Radiology
[{'content': 'Which of the following primary produces a Radio-opaque secondary in bone? \nSelect and explain. \nA. Prostate, B. Thyroid, C. Kidney, D. Breast', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Prostate', 'role': 'assistant'}]