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: Physiology
[{'content': 'Which one of the following is a regulatory protein of the muscle? \nSelect and explain. \nA. Troponin, B. Myosin, C. Actin, D. Protein-C', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]