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: Dental
The main component of keratins in the stratum corneum is 
Select and explain. 
A. Keratin polypeptide (68kD), B. K19 Keratin polypeptide (40kD), C. K12 Keratin polypeptide (40kD), D. K1 keratin polypeptide (68kD)
D: K1 keratin polypeptide (68kD)
Answer: D: K1 keratin polypeptide (68kD) 
Explanation: None