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
[{'content': 'Cholera toxin – \nSelect and explain. \nA. increase the levels of intracellular cyclic GMP, B. Act through opiate receptor, C. causes continued activation of adenyl cyclase, D. inhibit the enzyme phosphodiesterase', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]