<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 25-year-old man comes to the physician because of diarrhea, bloating, nausea, and vomiting for the past 3 days. He describes his stool as soft, frothy, and greasy. He denies seeing blood in stool. The patient went on a hiking trip last week and drank fresh water from the stream. Three months ago, he was on vacation with his family for 2 weeks in Brazil, where he tried many traditional dishes. He also had watery diarrhea and stomach cramping for 3 days during his visit there. He has no history of serious illness. He takes no medications. The patient appears dehydrated. His temperature is 37C 98.6F, blood pressure is 10060 mm Hg, pulse is 80min, and respirations are 12min. Examination shows dry mucous membranes and diffuse abdominal tenderness. Microscopy of the stool reveals cysts. Which of the following is the most appropriate next step in management?? A: Ciprofloxacin therapy, B: Octreotide therapy, C: Metronidazole therapy, D: Trimethoprim-sulfamethoxazole therapy, E: Supportive treatment only,  <response>: Based on the description in the question stem, this patient likely has gastroenteritis caused by an infectious agent acquired during recent travel. The symptoms of diarrhea, bloating, nausea, vomiting, and abdominal cramping along with the finding of cysts on stool microscopy are consistent with giardiasis given his recent travel to Brazil. Giardia is a common cause of travelers diarrhea. The most appropriate next step would be to treat with an anti-parasitic medication targeting Giardia, rather than antibiotics targeting bacteria.C: Metronidazole therapy 