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
Which of the following statements best describes a hapten? 
Select and explain. 
A. Haptens activate T cells, B. Penicillin is a hapten, C. Haptens do not react with specific antibody, D. Haptens bind the major histocompatibility complex
B: Penicillin is a hapten
Answer: B: Penicillin is a hapten 
Explanation: Haptens react with antibodies but they are not immunogenic. They do not activate T cells and cannot bind the major histocompatibility complex. Penicillin is a hapten and can cause severe life threatening allergic reaction.