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: Physiology
The four major bile acids found in humans are synthesized from: 
Select and explain. 
A. Cholesterol, B. Amino acids, C. Bilirubin, D. Protein
A: Cholesterol
Answer: A: Cholesterol 
Explanation: When considering bile as a digestive secretion, it is the bile acids that represent the most impoant components. They are synthesized from cholesterol and secreted into the bile conjugated to glycine or taurine, a derivative of cysteine. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 25. Overview of Gastrointestinal Function & Regulation. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.