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
Antigen - Antibody reactions occurs at its best at 
Select and explain. 
A. Prozone, B. Postzone, C. Zone of equivalence, D. All of the above
C: Zone of equivalence
Answer: C: Zone of equivalence 
Explanation: Zone of equivalence - Ag and Ab level equal thus, best.