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': 'During skeletal muscle contraction: \nSelect and explain. \nA. A band shorten, B. Both H and I band shorten, C. Both A and I band shorten, D. Both A and H band shorten', 'role': 'user'}, {'content': 'Answer: B \nExplanation: During\xa0 muscle\xa0contraction,\xa0 two Z lines come\xa0 closer;\xa0 the\xa0 length\xa0 of\xa0 the\xa0 ‘A\xa0 band’\xa0remains constant\xa0whereas\xa0the\xa0length of\xa0H and I band decreases. The M line becomes\xa0more prominent.', 'role': 'assistant'}]