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: Psychiatry
Fluoxetine is a potent reuptake blocker of this substance? 
Select and explain. 
A. Morphine, B. Serotonin, C. Norepinephrine, D. Cholecystokinin
B: Serotonin
Answer: B: Serotonin 
Explanation: Serotonin