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
Bismuth compounds are incorporated in root canal filling materials because they are: 
Select and explain. 
A. Radio-opaque, B. Germicidal, C. Radiolucent, D. Adhesive
A: Radio-opaque
Answer: A: Radio-opaque 
Explanation: None