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': 'Contrast used in barium enema is – \nSelect and explain. \nA. Barium oxide, B. Barium sulphide, C. Barium sulphate, D. Lead sulphate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Barium sulfate is the traditional gastrointestinal contrast medium of choice. It is cheap and readily available, and its high density provides excellent contrast and definition. It is not absorbed by the gut and can, therefore, be used anywhere in the bowel.', 'role': 'assistant'}]