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
Prozone phenomenon is due to-a) Excess antigenb) Excess antibodyc) Hyperimmune reactiond) Disproportionate antigen-antibody levels 
Select and explain. 
A. bd, B. d, C. ab, D. ac
A: bd
Answer: A: bd 
Explanation: None