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
[{'content': 'Binding of gp 120 causes: \nSelect and explain. \nA. Infection of target cell, B. Facilitation of co-receptor, C. Fusing of virus and target cell, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b. Facilitation of co-receptor', 'role': 'assistant'}]