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: Medicine
[{'content': 'It is a threadlike structure that extends from one end of the muscle fiber to another: \nSelect and explain. \nA. Sarcomere, B. Sarcolemma, C. Myofibril, D. Myofilament', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Option C:\xa0Myofibrils\xa0are composed of long proteins including actin, myosin, and titin, and other proteins that hold them together. These proteins are organized into thick and thin filaments called myofilaments, which repeat along the length of the myofibril in sections called sarcomeres.\nOption A:\xa0Sarcomere\xa0is the basic unit of striated muscle tissue.\nOption B:\xa0Sarcolemma\xa0is the fine transparent tubular sheath that envelops the fibers of skeletal muscles.\nOption D:\xa0Myofilaments\xa0are the filaments of myofibrils, constructed from proteins, principally myosin or actin.', 'role': 'assistant'}]