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: Pathology
Which of the following is the most abundant protein in animal world? 
Select and explain. 
A. Keratin, B. Elastin, C. Collagen, D. None of the above
C: Collagen
Answer: C: Collagen 
Explanation: Collagen is the most common protein in the animal world, providing the extracellular framework for all multicellular organisms. Ref: Robbins 8th edition Chapter 3.