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
Which of the following 5-HT3 blockers has highest receptor affinity - 
Select and explain. 
A. Ondansetron, B. Granisetron, C. Dolasetron, D. Palonosetron
D: Palonosetron
Answer: D: Palonosetron 
Explanation: Ans. is 'd' i.e., Palonosetron Palonosetron has maximum affinity for 5HT3 receptor.