Tetrodotoxin (TTX) Is Generally Associated with Pufferfish, Which in Fact

Tetrodotoxin (TTX) is generally associated with pufferfish, which in fact gain it from symbiotic bacteria residing in them. Interestingly, the pufferfish themselves aren't affected by this neurotoxin. The most plausible explanation for the fish's insensitivity to TTX is

A) the fish lack neurons.
B) the fish have neurons, but with very short axons that enable them to rely entirely on electrical conduction based on local passive current flow.
C) the fish lack voltage-gated sodium channels .
D) the fish have voltage-gated sodium channels, but they have a slightly different sequence from voltage-gated sodium channels found in other organisms, and this difference affects TTX's ability to bind the channel.