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
In the presence of vasopressin, which part of nephrons become more permeable to water 
Select and explain. 
A. Proximal tubule., B. Loop of Henle., C. Distal tubule., D. Cortical collecting duct.
D: Cortical collecting duct.
Answer: D: Cortical collecting duct. 
Explanation: In the presence of enough vasopressin to produce maximal antidiuresis, water moves out of the hypotonic fluid entering the cortical collecting ducts into the interstitium of the cortex, and the tubular fluid becomes isotonic.