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
Binding of gp 120 causes: 
Select and explain. 
A. Infection of target cell, B. Facilitation of co-receptor, C. Fusing of virus and target cell, D. None
B: Facilitation of co-receptor
Answer: B: Facilitation of co-receptor 
Explanation: Ans. b. Facilitation of co-receptor