<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 47-year-old man presents with recurrent epigastric pain and diarrhea. He has had these symptoms for the last year or so and has been to the clinic several times with similar complaints. His current dosage of omeprazole has been steadily increasing to combat his symptoms. The pain seems to be related to food intake. He describes his diarrhea as watery and unrelated to his meals. Blood pressure is 11580 mm Hg, pulse is 76min, and respiratory rate is 19min. He denies tobacco or alcohol use. He does not take any medications. An upper endoscopy is performed due to his unexplained and recurrent dyspepsia and reveals thickened gastric folds with three ulcers in the first part of the duodenum, all of which are negative for H. pylori. Which of the following is the best next step in this patients management?? A: Serum calcium levels, B: Fasting serum gastrin levels, C: Secretin stimulation test, D: CT scan of the abdomen, E: Somatostatin receptor scintigraphy,  <response>: Based on the patients symptoms of recurrent epigastric pain and diarrhea, as well as the endoscopic findings of thickened gastric folds and duodenal ulcers negative for H. pylori, the differential diagnosis includes Zollinger-Ellison syndrome. Zollinger-Ellison syndrome is caused by gastrin-secreting tumors, usually found in the pancreas or duodenum. Elevated fasting serum gastrin levels can help confirm the diagnosis. A secretin stimulation test can also be used to diagnose Zollinger-Ellison syndrome by assessing gastrin levels before and after secretin administration. The other tests listed may be helpful in evaluating the extent of disease but are not the best next step in diagnosis.B: Fasting serum gastrin levels 