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: Pharmacology
[{'content': 'In which of the following categories are ephedrine, tyramine and amphetamine classified: \nSelect and explain. \nA. Anticholinesterases, B. Alpha-adrenergic blocking agents, C. Indirect acting sympathomimetics, D. Direct acting sympathomimetics', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]