This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Membrane attack complex is formed by all except? 
Select and explain. 
A. C3, B. C5, C. C7, D. C9
A: C3
Answer: A: C3 
Explanation: Ans. (a) C3