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
[{'content': 'HIV RNA by PCR can detect as low as \nSelect and explain. \nA. 30 copies viral RNA/ml of blood, B. 40 copies viral RNA/ml of blood, C. 50 copies of viral RNA/ml of blood, D. 60 copies of viral RNA/ml of blood', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 40 copies viral RNA/ml of blood", 'role': 'assistant'}]