You are answering a USMLE-style medical question. Question: A 70-year-old man presents to the Emergency Department after 3 days of shortness of breath, orthopnea, and lower limb edema. His personal history is significant for a myocardial infarction 6 years ago that required revascularization and hypertension. His medication consists of simvastatin and lisinopril. In the ED, he has a blood pressure of 100/80 mm Hg, a pulse of 88/min, a respiratory rate of 28/min, and a temperature of 36.5°C (97.7°F). On physical examination, he has jugular vein distention, displaced point of maximal impulse (PMI), an S4-gallop, a holosystolic murmur, and 2+ pitting edema up to the mid calf. He is started on furosemide, carvedilol, and oxygen therapy. After 6-hours of continued therapy, his blood pressure remains low, and his serum creatinine is found to be 1.9 mg/dL. Which of the following test would be more useful to differentiate between prerenal and intrinsic kidney disease? Options: A) Sulfosalicylic acid test B) Urine sodium content C) Fractional excretion of urea (FEUrea) D) Nitrates in urine Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.