question: Q:A 24-year-old man presents to the postoperative unit after undergoing an appendectomy following 2 episodes of acute appendicitis. He complains of nausea and vomiting. On physical examination, his temperature is 36.9°C (98.4ºF), pulse rate is 96/minute, blood pressure is 122/80 mm Hg, and respiratory rate is 14/minute. His abdomen is soft on palpation, and bowel sounds are normoactive. Intravenous ondansetron is administered, and the patient reports relief from his symptoms. Which of the following best explains the mechanism of action of this drug?? 
  {'A': 'Inhibition of gastroesophageal motility', 'B': 'Inhibition of dopamine receptors on chemoreceptor trigger zone (CTZ)', 'C': 'Stimulation of 5-HT3 receptors on the nucleus of the tractus solitarius', 'D': 'Stimulation of intestinal and colonic motility', 'E': 'Inhibition of serotonin receptors on the vagal and spinal afferent nerves from the intestines'},