This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
[{'content': 'The major source of calcium for contraction of skeletal muscle is: \nSelect and explain. \nA. ECF, B. Cytosol, C. Mitochondria, D. Sarcoplasmic reticulum (SR)', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. D. sarcoplasmic reticulum (SR)Skeletal muscle depends on the SR as the major source of calcium. Cardiac muscle and smooth muscle depend on influx of calcium from ECF and Ca-induced calcium release for contraction.', 'role': 'assistant'}]