Urea diffuses out of the __________ , and into the __________ .
a. proximal tubule, distal tubule
b. proximal tubule, descending limb of the loop of Henle
c. descending limb of the loop of Henle, ascending limb of the loop of Henle
d. ascending limb of the loop of Henle, descending limb of the loop of Henle
e. collecting duct, descending limb of the loop of Henle
Answer: E