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
Transfer factor is an example of: 
Select and explain. 
A. Artificial active immunity, B. Natural active immunity, C. Adoptive immunity, D. Artificial passive immunity
C: Adoptive immunity
Answer: C: Adoptive immunity 
Explanation: Acquired by injection of immunologically competent T-lymphocytes known as Transfer factor
Used for treatment when the CMI is low, e.g. Lepromatous leprosy.