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
Which is the longest DNA of hepatitis B virus ? 
Select and explain. 
A. P gene, B. X gene, C. S gene, D. C gene
A: P gene
Answer: A: P gene 
Explanation: Ans. is 'a' i.e., P gene