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 of the cases of Listeria are due to serovar ? 
Select and explain. 
A. 2, B. 4a, C. 4b, D. 6
C: 4b
Answer: C: 4b 
Explanation: Ans. is `c' i.e., 4b