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: Physiology
Sodium channels are specifically blocked by ? 
Select and explain. 
A. Nifedipine, B. Tetra Ethyl lead, C. Tetradotoxin, D. Choline
C: Tetradotoxin
Answer: C: Tetradotoxin 
Explanation: C i.e. Tetradotoxin