This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Granisetron is a: \nSelect and explain. \nA. 5HT3 agonist, B. 5HT3 antagonist, C. 5HT2 antagonist, D. 5HT3 agonist', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 5HT3 antagonist', 'role': 'assistant'}]