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
Granisetron is a: 
Select and explain. 
A. 5HT3 agonist, B. 5HT3 antagonist, C. 5HT2 antagonist, D. 5HT3 agonist
B: 5HT3 antagonist
Answer: B: 5HT3 antagonist 
Explanation: 5HT3 antagonist