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, has antiemetic properties because of: 
Select and explain. 
A. Dopaminergic receptor — blocking actions, B. Gabamimetic actions, C. Gaba-inhibitory actions, D. Serotonin receptor-blocking action
D: Serotonin receptor-blocking action
Answer: D: Serotonin receptor-blocking action 
Explanation: Granisetron is 5-HT3 antagonist and is 10 times more potent than ondansetron, and probably more effective during the repeat cycle of chemotherapy. The weak 5-HT4 blockade seen with ondansetron  has not been detected in granisetron. lts plasma t½ is longer (8-12 hrs) and it needs to be given only twice on the day of chemotherapy.