This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gall Bladder & Bile Ducts, Subject name: Surgery
[{'content': 'Identity the type of Stone shown below: \nSelect and explain. \nA. Mixed, B. Cholesterol, C. Brown, D. Black', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. (b) Cholesterol Cholesterol: Pale yellow - Only Cholesterol is present 15% are Radio opaque* Black: Hard Stone- Insoluble Bilirubin Pigment polymer+ Calcium Phosphate + Calcium Carbonate Brown: Soft friable like Earth sand- Calcium Bilirubinate+ Calcium Palmitate+ Calcium Stearate+CholesterolBlack stones are 60% radio opaque Brown stones are never radio opaquePigment stone is the name given when the stone contains Cholesterol <30%', 'role': 'assistant'}]