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
Hereditary angioneurotic edema is due to deficiency of 
Select and explain. 
A. C1 deficiency, B. C2 and C4 deficiency, C. C1 esterase inhibitor, D. C9 deficiency
C: C1 esterase inhibitor
Answer: C: C1 esterase inhibitor 
Explanation: C1 esterase inhibitor causes Hereditary angioneurotic edema.