A 78-year-old man presents with fatigue and difficulty with bladder emptying. Examination reveals a distended bladder but is otherwise unremarkable. The blood urea nitrogen (BUN) is 88 mg/dL (31.4 mmol/L); the creatinine is 2.8 mg/dL (247.5 μmol/L). This clinical assessment is most consistent with .
A. Prerenal azotemia
B. Acute glomerulonephritis
C. Acute tubular necrosis
D. Postrenal azotemia

How is the central idea developed further? (a) the author elaborates on the treatments for allergies in adults and how they work. (b) the author quotes the reactions of experts and the methods used to conduct the study. (c) the author compares the different rates of food allergies shown in children and adults. (d) the author indicates the limitations of the study because of differences in health care.