This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Structure & Function of Proteins), Subject name: Biochemistry
Keratin contains - 
Select and explain. 
A. Arginine, B. Histidine, C. Lysine, D. All
D: All
Answer: D: All 
Explanation: Ans. is 'd' i.e., All