<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 21-year-old male presents after several days of flatulence and greasy, foul-smelling diarrhea. The patient reports symptoms of nausea and abdominal cramps followed by sudden diarrhea. He says that his symptoms started after he came back from a camping trip. When asked about his camping activities, he reports that his friend collected water from a stream, but he did not boil or chemically treat the water. His temperature is 98.6F 37C, respiratory rate is 15min, pulse is 67min, and blood pressure is 12298 mm Hg. Stool is sent for microscopy which returns positive for motile protozoans. Which of the following antibiotics should be started in this patient?? A: Erythromycin, B: Ciprofloxacin, C: Metronidazole, D: Vancomycin, E: Cephalexin,  <response>: This is a clinical case of a 21-year-old male with diarrhea, nausea, abdominal cramps, and positive stool microscopy for motile protozoans after drinking untreated stream water while camping. The history and symptoms are most consistent with giardiasis given the exposure to untreated stream water and subsequent gastrointestinal symptoms. Metronidazole is the first-line treatment for giardiasis. Erythromycin may also be used but is not preferred. Ciprofloxacin, vancomycin, and cephalexin are not appropriate treatments.C: Metronidazole 