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: Surgery
Silk is which class of suture? 
Select and explain. 
A. 1, B. 2, C. 3, D. None
A: 1
Answer: A: 1 
Explanation: United States of pharmacopeia classification of suture
Class 1...silk
Class 2...cotton
Class 3...metal suture