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: Medicine
Brown type gallstones are formed due to: 
Select and explain. 
A. Hypercholesterolemia, B. Long standing hemolysis, C. Chronic biliary infection, D. Drugs
C: Chronic biliary infection
Answer: C: Chronic biliary infection 
Explanation: Pigment stones are composed of calcium bilirubinate and are classified into "black" and "brown" types, the latter forming secondary to chronic biliary infection. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Pages 2616-17