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
A person has unprotected sex 3 weeks back. To rule out HIV infection the best test is: 
Select and explain. 
A. P24 antigen assay, B. ELISA, C. Western blot, D. Lymphnode biopsy
A: P24 antigen assay
Answer: A: P24 antigen assay 
Explanation: Ans. a. P24 antigen assay