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
In a patient only anti HBs Ag is positive in serum, all other markers are negative. This indicates ? 
Select and explain. 
A. Acute hepatitis, B. Chronic active hepatitis, C. Persistent carrier, D. Hepatitis B vaccination
D: Hepatitis B vaccination
Answer: D: Hepatitis B vaccination 
Explanation: Ans. is 'd' i.e., Hepatitis B vaccination