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': 'Possible source of “SECOND SIGNAL” to a bound Bcell by specific antigen include \nSelect and explain. \nA. EB virus, B. Endotoxin, C. Antigen specific T-cell, D. plasma cells.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]