This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gallbladder, Subject name: Surgery
Gallstones do not contain: 
Select and explain. 
A. Oxalate, B. Cholesterol, C. Phosphate, D. Carbonate
A: Oxalate
Answer: A: Oxalate 
Explanation: Gallstones In the USA and Europe, 80% are cholesterol or mixed stones, whereas in Asia, 80% are pigment stones Cholesterol or mixed stones - 51-99% pure cholesterol Pigment stone contains <30% cholesterol Black stones - Insoluble bilirubin polymer + calcium phosphate + calcium bicarbonate Brown pigment stones- calcium bilirubinate+ calcium palmitate + calcium stearate+ cholesterol