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': 'Bismuth compounds are incorporated in root canal sealer materials because they are: \nSelect and explain. \nA. Radio-opaque, B. Germicidal, C. Radiolucent, D. Adhesive', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Root canal sealers should be radiopaque, so that it can be visualized in the radiograph.\nRadiopacity is provided by salts of heavy metals such as silver, barium and bismuth.', 'role': 'assistant'}]