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': 'Functional unit of kidney is: \nSelect and explain. \nA. Nephron, B. Glomerulus, C. Collecting ducts, D. Loop of Henle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]