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': 'Which of the following allows binding of HIV to CD 4 cells  - \nSelect and explain. \nA. gp 120, B. gp 41, C. Proteins formed by expression of gag gene, D. ccR5', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]