This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
By definition pigment stone Contain how much percentage of cholesterol 
Select and explain. 
A. <10, B. <20, C. <30, D. <60
C: <30
Answer: C: <30 
Explanation: Pigment stone is the name used for stones containing <30% cholesterol Classification of gallstones Cholesterol Black pigment Brow pigment Location Gall bladder and bile duct Gall bladder and bile duct Bile ducts Major constituent Cholesterol Bilirubin pigment polymer Calcium bilirubinate Consistency Crystalline with nucleus Hard Soft, Friable % Radiopaque 15% 60% 0% Ref: Bailey and love 27th edition Pgno :1120