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: Medicine
Which is the usual marker for detection of hepatitis- 
Select and explain. 
A. HBs Ag, B. HBs Ab, C. HBc Ag, D. HBc Ab
A: HBs Ag
Answer: A: HBs Ag 
Explanation: None