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
Possible source of “SECOND SIGNAL” to a bound Bcell by specific antigen include 
Select and explain. 
A. EB virus, B. Endotoxin, C. Antigen specific T-cell, D. plasma cells.
C: Antigen specific T-cell
Answer: C: Antigen specific T-cell 
Explanation: None