question: Q:A 15-year-old man presents with his father to the urgent care department with a 5-day history of frequent diarrhea, occasionally mixed with streaks of blood. Stool cultures are pending, but preliminary stool samples demonstrate fecal leukocytes and erythrocytes. The patient's vital signs are within normal limits, and he is started on outpatient therapy for presumed Shigella infection. Which of the following was the young man most likely started on?? 
  {'A': 'Oral erythromycin', 'B': 'Oral metronidazole', 'C': 'Oral vancomycin', 'D': 'An oral quinolone', 'E': 'Oral trimethoprim-sulfamethoxazole (TMP-SMX)'},