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': 'Substance utilized for barium meal follow through study: September 2011 \nSelect and explain. \nA. Barium carbonate, B. Barium sulphate, C. Barium oxide, D. Barium hydroxide', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B: Barium sulphate Since there is no natural contrast in the alimentary tract, its radiographic demonstration required the use of aificial contrast medium Barium sulphate, through which X-rays can not pass, is the contrast universally employed in performing alimentary tract studies', 'role': 'assistant'}]