This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Functional unit of muscle: \nSelect and explain. \nA. Sarcomere, B. Actin, C. Myosin, D. Troponin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Functional unit of muscle is : sarcomere It is the pa of myofibril present between two succsive z lines. Ref: Guyton and Hall textbook of medical physiology 12th edition, page number:86,87', 'role': 'assistant'}]