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: Microbiology
First chemical barrier encountered by microorganism for common exposed sites - 
Select and explain. 
A. Lysozyme, B. Acidic pH, C. Skin, D. Lactose
B: Acidic pH
Answer: B: Acidic pH 
Explanation: None