Which one of the following is a 5-HT3 antagonist?

(A) Ondansetron ANTAGONISTS IN CHEMOTHERAPY-INDUCED NAUSEA/EMESISDRUGCHEMICAL NATURERECEPTOR INTERACTIONST1/2DOSE (IV)OndansetronCarbazole derivative5-HT3 antagonist and weak 5-HT4 antagonist3.9 hours0.15 mg/kgGranisetronIndazole5-HT3 antagonist9-11.6 hours10 ug/kgDolasetronIndole moiety5-HT3 antagonist7-9 hours0.6-3 mg/kgPalonosetronIsoquinoline5-HT3 antagonist; highest affinity for 5-HT3 receptor in this class40 hours0.25 mgRamosetronBenzidazolyl derivative5-HT3 antagonist5.8 hours300 ug/kg> Ondansetron is a serotonin 5-HT3 receptor antagonist used mainly to treat nausea and vomiting following chemotherapy. Its effects are thought to be on both peripheral and central nerves.> One part is to reduce the activity of the vagus nerve, which is a nerve that activates the vomiting center in the medulla oblongata, the other is a blockage of serotonin receptors in the chemoreceptor trigger zone.> It does not have much effect on vomiting that is due to motion sickness. This drug does not have any effect on dopamine receptors or muscarinic receptors.> 5-HT3-Receptor Antagonists: Chemistry, Pharmacological Effects, and Mechanism of Action.> Ondansetron (ZOFRAN) is the prototypical drug in this class. Since their introduction in the early 1990s, the 5-HT3-receptor antagonists have become the most widely used drugs for chemotherapy-induced emesis. Other agents in this class include granisetron (KYTRIL), dolasetron (ANZEMET), palonosetron (ALOXI; intravenous use only) and tropisetron> The differences among these agents are related mainly to their chemical structures, 5-HT3 receptor affinities & pharmacokinetic profiles