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
Most common serotype of listeria causing infections: 
Select and explain. 
A. 1/2a, B. 1/3a, C. 1/3b, D. 1/2c
A: 1/2a
Answer: A: 1/2a 
Explanation: Ans. is. 'a' i. e., 1/2a