<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 37-year-old woman presents to the Emergency Department after 8 hours of left sided flank pain that radiates to her groin and pelvic pain while urinating. Her medical history is relevant for multiple episodes of urinary tract infections, some requiring hospitalization, and intravenous antibiotics. In the hospital, her blood pressure is 12583 mm Hg, pulse of 88min, a respiratory rate of 28min, and a body temperature of 36.5C 97.7F. On physical examination, she has left costovertebral tenderness and lower abdominal pain. Laboratory studies include a negative pregnancy test, mild azotemia, and a urinary dipstick that is positive for blood. Which of the following initial tests would be most useful in the diagnosis of this case?? A: Fractional excretion of sodium FeNa, B: Renal ultrasonography, C: Contrast abdominal computed tomography, D: Urine osmolality, E: Blood urea nitrogen BUN: serum creatinine SCr ratio,  <response>: This is a clinical case about a 37-year-old woman presenting with left flank pain radiating to the groin, pelvic pain while urinating, history of recurrent UTIs, costovertebral tenderness, lower abdominal pain, azotemia, and hematuria. The key findings are left-sided flankabdominal pain, history of recurrent UTIs, hematuria, and azotemia. This presentation is most consistent with an acute pyelonephritis kidney infection. Choice A tests the fractional excretion of sodium which is not useful for diagnosing pyelonephritis. Choice B, renal ultrasonography, is a good initial test to evaluate for hydronephrosis or renal calculi which can cause pyelonephritis. This is likely the best initial test.Choice C, CT abdomen, provides more detailed imaging but ultrasonography is preferred as the initial test. CT would be considered if the ultrasound is non-diagnostic.Choice D, urine osmolality, is not useful for diagnosing pyelonephritis. Choice E, BUN:creatinine ratio, may be elevated in dehydration but is not specific for pyelonephritis.B: Renal ultrasonography 