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 among the following is the contractile unit of muscle? \nSelect and explain. \nA. Sarcomere, B. Sarcolemma, C. Myofibril, D. Sarcotubular System', 'role': 'user'}, {'content': "Answer: A \nExplanation: The basic contractile unit of skeletal muscle is the sarcomere. Sarcomeres are connected to each other by their Z lines. Each sarcomere contains an array of filaments that consist of actin and myosin molecules, which interact to produce contractile force. Ref: Medical Physiology: Principles for Clinical Medicine By Rodney A. Rhoades, Ph.D., David R. Bell, Ph.D., 2012, Page 141; Guyton's physiology 22nd edition, Page 73.", 'role': 'assistant'}]