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
Which of the following primary produces a Radio-opaque secondary in bone? 
Select and explain. 
A. Prostate, B. Thyroid, C. Kidney, D. Breast
A: Prostate
Answer: A: Prostate 
Explanation: Ans. Prostate