You are answering a USMLE-style medical question. Question: A 47-year-old woman presents to a physician for evaluation of vomiting and diarrhea for 2 days. Her symptoms began following a company picnic a few days ago. Initially, she was unable to tolerate any solids or liquids by mouth, but now has been able to drink sips of water. She had a mild headache, which was relieved with acetaminophen. The past medical history is unremarkable. She does not take any medications. The blood pressure is 120/60 mm Hg and the heart rate is 60/min. On examination, the mucous membranes are dry and the eyes are slightly sunken. Where is most of the sodium reabsorbed in this patient’s kidneys? Options: A) Distal tubule B) Descending limb of loop of Henle C) Proximal tubule D) Ascending limb of loop of Henle Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.