This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
The principal site of acidification of urine is 
Select and explain. 
A. Loop of henle, B. Collecting duct, C. DCT, D. PCT
B: Collecting duct
Answer: B: Collecting duct 
Explanation: The cells of the proximal and distal tubules secrete hydrogen ions. Acidification also occurs in the collecting ducts. The reaction that is primarily responsible for H+ secretion in the proximal tubules is Na+-H+ exchange. Na is absorbed from the lumen of the tubule and H is excreted. Ref: guyton and hall textbook of medical physiology 12 edition page number:504,505,506