This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Antigen-antibody reaction, Subject name: Microbiology
[{'content': 'Postzone phenomenon is seen in - \nSelect and explain. \nA. Antigen excess, B. Antibody excess, C. Equivalance zone, D. None of the above', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Antigen excess Antigen - antibody reaction || ||Ascending partPeakDescending part|||Prozone or zone of antibody excessZone of equivalencePost zone or zone of antigen excess", 'role': 'assistant'}]