This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
Which of the following for pain control in terminally ill cancer patients 
Select and explain. 
A. Pethidine, B. Fentanyl, C. Methodone, D. Remifentanyl
B: Fentanyl
Answer: B: Fentanyl 
Explanation: Fentanyl, also spelled fentanil, is an opioid used as a pain medication and together with other medications for anesthesia. Fentanyl is also used as a recreational drug, often mixed with heroin or cocaine. It has a rapid onset and effects generally last less than two hours. Ref: KD TRIPATHI 8TH ED.