TOEFL Listening: ETS-TOEFL听力机经 - 55H962U6XP5UFK9IP$

What evidence suggests that puffer fish do not make tetrodotoxin themselves? A. They die if their nerve cells are exposed to tetrodotoxin for long periods of time. B. They do not contain tetrodotoxin if they are raised in a controlled environment C. The steps that are necessary to produce tetrodotoxin are biologically complex. D. The chemicals required to synthesize tetrodotoxin are not found in ocean water