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': 'The principal site of acidification of urine is: \nSelect and explain. \nA. Distal convoluted tubule, B. Proximal convoluted tubule, C. Loop of Henle, D. Collecting duct', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Acidification occurs in collecting duct and DCT, but collecting duct is more important. Hence, answer is D>A.', 'role': 'assistant'}]