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': 'The effect of cholera toxin is mediated the stimulation of following second messenger: \nSelect and explain. \nA. cAMP, B. cGMP, C. Calcium-calmodulin, D. Acetylcholine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) cAMP', 'role': 'assistant'}]