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
All of the following belong to the group of microbial sensors, EXCEPT: 
Select and explain. 
A. TLRs, B. NOD-like receptors (NLRs), C. MDA-5, D. None of the above
D: None of the above
Answer: D: None of the above 
Explanation: When a pathogen enters the skin, it is confronted with macrophages and other phagocytic cells possessing "microbial sensors." There are three major groups of microbial sensors: (1) TLRs, (2) NOD-like receptors (NLRs), and (3) RIG-1 like helicases and MDA-5. Ref: Brooks G.F. (2013). Chapter 8. Immunology. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.