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': 'Window period" in HIV is defined as - \nSelect and explain. \nA. Period between infection and appearance of symptoms, B. Period between onset of infection and clinically detectable level of antibodies, C. Time between HIV positivity to AIDS, D. CD4 count <200', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Window period is a period between entry of virus to appearance of detectable Ab in serum', 'role': 'assistant'}]