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: Medicine
A toxin of clostridium tetanus, tetanospasmin causes muscular rigidity by blocking 
Select and explain. 
A. Gamma amino butyric acid, B. Dopamine, C. Serotonin, D. Glutamine
A: Gamma amino butyric acid
Answer: A: Gamma amino butyric acid 
Explanation: None